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  • CQRS &ndash; Questions and Concerns

    - by Dylan Smith
    I’ve been doing a lot of learning on CQRS and Event Sourcing over the last little while and I have a number of questions that I haven’t been able to answer. 1. What is the benefit of CQRS when compared to a typical DDD architecture that uses Event Sourcing and properly captures intent and behavior via verb-based commands? (other than Scalability) 2. When using CQRS what do you do with complex query-based logic? I’m going to elaborate on #1 in this blog post and I’ll do a follow-up post on #2. I watched through Greg Young’s video on the business benefits of CQRS + Event Sourcing and first let me say that I thought it was an excellent presentation that really drives home a lot of the benefits to this approach to architecture (I watched it twice in a row I enjoyed it so much!). But it didn’t answer some of my questions fully (I wish I had been there to ask these of Greg in person!). So let me pick apart some of the points he makes and how they relate to my first question above. I’m completely sold on the idea of event sourcing and have a clear understanding of the benefits that it brings to the table, so I’m not going to question that. But you can use event sourcing without going to a CQRS architecture, so my main question is around the benefits of CQRS + Event Sourcing vs Event Sourcing + Typical DDD architecture Architecture with Event Sourcing + Commands on Left, CQRS on Right Greg talks about how the stereotypical architecture doesn’t support DDD, but is that only because his diagram shows DTO’s coming up from the client. If we use the same diagram but allow the client to send commands doesn’t that remove a lot of the arguments that Greg makes against the stereotypical architecture? We can now introduce verbs into the system. We can capture intent now (storing it still requires event sourcing, but you can implement event sourcing without doing CQRS) We can create a rich domain model (as opposed to an anemic domain model) Scalability is obviously a benefit that CQRS brings to the table, but like Greg says, very few of the systems we create truly need significant scalability Greg talks about the ability to scale your development efforts. He says CQRS allows you to split the system into 3 parts (Client, Domain/Commands, Reads) and assign 3 teams of developers to work on them in parallel; letting you scale your development efforts by 3x with nearly linear gains. But in the stereotypical architecture don’t you already have 2 separate modules that you can split your dev efforts between: The client that sends commands/queries and receives DTO’s, and the Domain which accepts commands/queries, and generates events/DTO’s. If this is true it’s not really a 3x scaling you achieve with CQRS but merely a 1.5x scaling which while great doesn’t sound nearly as dramatic (“I can do it with 10 devs in 12 months – let me hire 5 more and we can have it done in 8 months”). Making the Query side “stupid simple” such that you can assign junior developers (or even outsource it) sounds like a valid benefit, but I have some concerns over what you do with complex query-based logic/behavior. I’m going to go into more detail on this in a follow-up blog post shortly. He also seemed to focus on how “stupid-simple” it is doing queries against the de-normalized data store, but I imagine there is still significant complexity in the event handlers that interpret the events and apply them to the de-normalized tables. It sounds like Greg suggests that because we’re doing CQRS that allows us to apply Event Sourcing when we otherwise wouldn’t be able to (~33:30 in the video). I don’t believe this is true. I don’t see why you wouldn’t be able to apply Event Sourcing without separating out the Commands and Queries. The queries would just operate against the domain model instead of the database. But you’d still get the benefits of Event Sourcing. Without CQRS the queries would only be able to operate against the current state rather than the event history, but even in CQRS the domain behaviors can only operate against the current state and I don’t see that being a big limiting factor. If some query needs to operate against something that is not captured by the current state you would just have to update the domain model to capture that information (no different than if that statement were made about a Command under CQRS). Some of the benefits I do see being applicable are that your domain model might end up being simpler/smaller since it only needs to represent the state needed to process commands and not worry about the reads (like the Deactivate Inventory Item and associated comment example that Greg provides). And also commands that can be handled in a Transaction Script style manner by the command handler simply generating events and not touching the domain model. It also makes it easier for your senior developers to focus on the command behavior and ignore the queries, which is usually going to be a better use of their time. And of course scalability. If anybody out there has any thoughts on this and can help educate me further, please either leave a comment or feel free to get in touch with me via email:

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  • How do I fix an overheating problem with an HP ENVY-4 ultrabook?

    - by ashutosh jain
    I have bought a new HP ENVY-4 ultrabook. It has an i5 processor, preinstalled windows7 and 2GB radeon graphics card. What happened was when I started using ubuntu it showed overheating. I ignored it but after a few days it burnt my laptop battery to 0% capacity. It was just one month old so I got the battery replaced for free. I tried installing linux mint but it also showed overheating. I tried fedora17 but it didn't installed fine. On windows it is running perfectly fine and it's not even heating a bit. Now anyone please suggest whats the problem with ubuntu and how can I overcome with it. I am a computer science guy so I can't work without linux and this machine is then like a waste for me.

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  • What is the problem git submodules are supposed to solve?

    - by Joshua Dance
    What is the problem that git submodules solve well? When should I use them? Or rather what is their use case? The only use of submodules that I have seen 'in the wild' has been when used to share code between multiple repositories. From what I have experienced, submodules do not appear to be ideally suited to this use case. You run into git update submodule woes and your history gets filled with updating submodule pointer commits. If the 'sharing code' use case is not best solved by submodules, what problems are?

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  • Graphics Driver problem, ATI Radeon HD 3200, small screen size and slows everything down.

    - by Arvind Jangid
    Regards. I am using a: 2009 Compaq Presario CQ40-415AU Notebook AMD Athlon X2 Dual core Processor 2.1 GHz 1024 MB L2 cache 3GB DDR2 RAM ATI Radeon + HD 3200 Graphics 256 MB, screen is 14 inch widescreen with resolution of 1280*800. I installed Ubuntu 12.04 LTS 32bit on my laptop. It works brilliantly until I installed graphics driver. When I installed the driver, the graphics became slow. Everything slowed down. Even the splash screen resolution changed to something like 640*480. I have liked Ubuntu since 9.10 and for the freedom it provides and its versatility, but graphics problem remains the same. I even installed Ubuntu on a 50 GB partition with 6 GB swap partition. My HDD is 320 GB. Please tell me what is wrong.

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  • Problem with Ogmo Editor (is Tiled Editor a solution?)

    - by Mentoliptus
    I made a level editor for a puzzle game with Ogmo Editor and gave it to our designer/level designer. When he downloaded and started Ogmo, his CPU went to 100%. I looked at my CPU usage while Ogmo is running, and it goes from 20% to 30% (which is also high for an application alike Ogmo). He has a Windows 7 VM running on his Mac and I have a normal Windows PC, can this be a problem? I found a thread on FlashFunk forum that confirms that Ogmo has CPU usage issues. Has anybody maybe solved this issue? The solution seems to use Tiled Editor, but I never used it before. Is it difficult to change a level editor from Ogmo to Tiled? Can they export in the same format (XML with CSV elements for my puzzle game)?

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  • Configuration server problem after changing /tmp mountpoint: how to solve?

    - by Aron Rotteveel
    I created a new partition on my hard drive because my /tmp partition was too small. I changed the mountpoint in /etc/fstab and rebooted. Every time I reboot, I get the following error message at the login screen: There is a problem with the configuration server. (/usr/lib/libgconf2-4/gconf-sanity-check-2 exited with status 256) When I log in, /tmp is mounted correctly and everything seems to work fine. When I reboot, the error shows again. When I change the /tmp mountpoint back to the old partition, the error message disappears. What could be causing this and how can I solve this issue?

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  • How can I get Ubuntu 12.04 to boot on a Gigabyte 990Fx MB (efi problem?)

    - by Jeffrey
    I am trying to install Ubuntu 12.04 on a home made system with a gigabyte 990Fxa MB. I can make it through the install process. It does not boot. Windows 7 does boot on the same machine. Suse 11.4 boots on the same machine. Suse 12.4 does not boot. I think there may be an issue with the EFI / GPT system. I know very little about these systems. I really expected the machine to boot. What can I do to get the system to boot? Please direct me to a path to trouble shoot this problem. thanks Jeffrey

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  • Unity3D problem. Bullets fall down instead of flying like they should

    - by user2342080
    I used this tutorial as a reference. http://www.youtube.com/watch?v=3L8eaoyZ0Go My problem is that whenever I play the game, EVERYTHING works but the bullets. It just falls down instead of flying forward. This is the flash version of the game: http://v1k.me/swf/ Can some one help me out? Should I upload the project? This is my "Shoot.js": public var bulletPrefab : Transform; public var bulletSpeed : float = 20; function Update() { if(Input.GetMouseButton(0)) { if(bulletPrefab || bulletSpeed) { var bulletCreate = Instantiate(bulletPrefab, GameObject.Find("SpawnPoint").transform.position, Quaternion.identity); bulletCreate.rigidbody.AddForce(transform.forward * bulletSpeed); } } }

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  • HP 530 Wireless problem. Bad communication with access point

    - by foxy
    I installed Ubuntu 11.10 on HP 530 and to make Wireless work installed STA driver from jockey (obviously proprietary) and, since it didn't work also installed their driver from HP website via ndiswrapper. After this (and a reboot) I see the WiFi indicator glowing, like it should be, and I am able to find local access points. But when I try to connect to mine personal one with WPA 2 security (with password) it hangs at authentification (I'm using wicd to manage wifi), and after a minute or so (I guess timeout of request happens) it says I have a wrong password (it is 100% correct). What might be the problem here? Yesterday I was able to connect to access point by changing type of encryption from passphrase to preshared key but didn't have internet access. Now, after reboot, I can't connect there again.

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  • Will adding q&a help my site's rankings, and if so, what are the implications of a sub-domain for q&a rather than a path on the site? [closed]

    - by ElHaix
    Possible Duplicate: Subdomain versus subdirectory One of our web properties is doing quite well without any additional links being created on the site, and our link inventory is tightly managed - no user-generated links. To introduce a community aspect to the site, we want to implement a q&a forum. Once in place, new links will populate our link inventory with keywords that are not necessarily targeted to the site. With the q&a on a sub-domain, would that not affect the main site's rankings? What's the best approach for this?

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  • Can you tell whether I have a hardware or software problem with a DVD-ROM drive?

    - by user8934
    Trying to copy the content of a DVD on a Asrock ION 330 running Maverick, i.e. with: dd if=/dev/sr0 of=dvdcopy ...I get errors in /var/log/messages: Jan 15 17:18:15 asrock kernel: [ 2616.445966] sr 1:0:0:0: [sr0] Unhandled sense code Jan 15 17:18:15 asrock kernel: [ 2616.445975] sr 1:0:0:0: [sr0] Result: hostbyte=DID_OK driverbyte=DRIVER_SENSE Jan 15 17:18:15 asrock kernel: [ 2616.445984] sr 1:0:0:0: [sr0] Sense Key : Medium Error [current] Jan 15 17:18:15 asrock kernel: [ 2616.445994] sr 1:0:0:0: [sr0] Add. Sense: Id CRC or ECC error Jan 15 17:18:15 asrock kernel: [ 2616.446004] sr 1:0:0:0: [sr0] CDB: Read(10): 28 00 00 00 00 02 00 00 02 00 I'd tell it is a hardware problem, but it happens with various DVDs and on a second PC, also running Maverick... Both the PCs previously ran Lucid, same problems.

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  • Missing launcher, top panel without icons, an ATI driver problem?

    - by jlotero
    After upgrading to Ubuntu 11.10, the following problems occurs when accesing in ubuntu mode (3D): the launcher is missing, top panel without icons on the right side, and I can only restart with Terminal (Alt-T and then sudo reboot). No problems in 2D. It occurs on my PC with AMD Athlon (tm) II X4 640 Processor, Radeon HD5670 and both with the 32-bit and 64 bits versions of Ubuntu. Both versions work well on an older PC with AMD Athlon 64 x2 Dual Core 4200 + processor, and an Nvidia integrated graphics card (C61 GeForce 6150SE nForce 430). Could it be a problem with the ATI driver?

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  • If there's no problem treating a statement as an expression, why was there a distinction in the first place in some programming languages?

    - by cdmckay
    Why do we have the distinction between statements and expressions in most programming languages? For example, in Java, assuming f and g return ints, this still won't compile because it's a statement and statements don't return values. // won't compile int i = if (pred) { f(x); } else { g(x); } but in Scala, it's very happy with treating if as an expression. // compiles fine val i: Int = if (pred) f(x) else g(x) So if there's no problem treating an if statement as an expression, why was there a distinction in the first place?

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  • Booting but not rebooting from external USB hard drive, what could be the problem?

    - by user8276
    I have a Dell Inspiron 6400 laptop with a dead internal hard drive controller. It boots perfectly from CD or USB. I therefore removed the internal hard drive and installed Ubuntu 10.10 Maverick onto an external USB hard drive. It boots and runs perfectly when doing a "cold start" of the PC. However, when I choose restart/reboot in the Ubuntu menu (e.g. after an update), I get this error message from the BIOS: "No bootable devices, strike f1 to retry boot, f2 for setup utility, press f5 to run onboard diagnostics". I can make the system boot again by pressing f2 or f5 and exiting the utility without having done anything. Or, I can simply power off the system and do a new "cold start". Does anyone know the likely reason for this problem and how to fix it. It is not a big issue but an annoyance that I would like to fix if possible.

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  • Where would you start if you were trying to solve this PDF classification problem?

    - by burtonic
    We are crawling and downloading lots of companies' PDFs and trying to pick out the ones that are Annual Reports. Such reports can be downloaded from most companies' investor-relations pages. The PDFs are scanned and the database is populated with, among other things, the: Title Contents (full text) Page count Word count Orientation First line Using this data we are checking for the obvious phrases such as: Annual report Financial statement Quarterly report Interim report Then recording the frequency of these phrases and others. So far we have around 350,000 PDFs to scan and a training set of 4,000 documents that have been manually classified as either a report or not. We are experimenting with a number of different approaches including Bayesian classifiers and weighting the different factors available. We are building the classifier in Ruby. My question is: if you were thinking about this problem, where would you start?

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  • Ubuntu 10.10 booting but not rebooting from external USB hard drive, what could be the problem?

    - by user8276
    I have a Dell Inspiron 6400 laptop with a dead internal hard drive controller. It boots perfectly from CD or USB. I therefore removed the internal hard drive and installed Ubuntu 10.10 Maverick onto an external USB hard drive. It boots and runs perfectly when doing a "cold start" of the PC. However, when I choose restart/reboot in the Ubuntu menu (e.g. after an update), I get this error message from the BIOS: "No bootable devices, strike f1 to retry boot, f2 for setup utility, press f5 to run onboard diagnostics". I can make the system boot again by pressing f2 or f5 and exiting the utility without having done anything. Or, I can simply power off the system and do a new "cold start". Does anyone know the likely reason for this problem and how to fix it. It is not a big issue but an annoyance that I would like to fix if possible.

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  • Log in sound is playing, but no sound during gnome desktop session.What's the problem?

    - by user14376
    When i installed ubuntu, everything was great. But one day, i heard the login sound but no sound on the desktop session. This happens every time. I have reinstalled sound drivers several times, checked speakers are not mute, checked alsamixer, saw all the troubleshooting tips on the net, checked user privileges too but of no help. anyone knows the answer? Please help!!!!! I have ubuntu 10.4LTS and alc662 sound chip. My computer is detecting the sound card and no problems with my speakers.This maybe a bug but i cannot report as i don't know if this will repeat(I atleast have to solve the problem first).

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  • How to solve this problem without the use of if-else statements?

    - by kira
    I have just started my C++ lecture class. And the teacher has given us the following assignment. Write a program that determines whether a number is even or odd. The logic I would use for the program is. Get input a. Store a % 2 as b. If b is 0, then b is even, else b is odd. The catch though, is that we have to write the program without the use of a if-else statement. I have been thinking on how to approach the problem for the past few hours, but I have no clue what to do. Any hints or suggestions?

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  • Is it a good idea to always use Google as the first step to solving a problem? [closed]

    - by The Rubber Duck
    Possible Duplicate: Importance of learning to google efficiently for a programmer? Avoiding lengthy discussions, as a senior level student in CS, how can I get away from Googling problems I run into? I find myself using it too much; I seemingly reach for the instant answer and then blindly copy and paste code, hoping it works. Anyone can do that. I've read the related threads about being a better programmer, but mostly those recommend practicing on pet projects, which I have done, but again I feel EVERY wall encountered, from design through completion, was hurdled with Google. Do professionals instantly "research" their problem? Or do you guys step back and try and figure it out yourselves? I'm talking about both 'algorithm/design' problems as well as compiler issues.

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  • Is there a problem if I don't setup google analytics in my website?

    - by sagar
    is there a problem if I don't setup google analytics in my website? I have read lot of articles describing use of google analytics but I have not added it in my site. In Cpanel I can check all things like stats, unique visitor etc and in google analytics its almost same but if I want sponsor for my site then is it necessary to have google analytics? or can cpanel stats be shown to sponsor? Thanks for reading! I hope I get an answer!

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  • Found a better solution to a problem at work - should I deter from posting the code snippet online?

    - by Calmarius
    I think most of us, programmers, used Stack Overflow to solve every day problems: looked for an efficient algorithm to do something. Now imagine a situation: you have a problem to solve. Googled a bit, found a StackOverflow question but you are not really satisfied with the answers so far. So you have to do your own research: you need to do it because you want it in the company's app. Eventually after some hours you have found the better solution. You're happy, you added it to the company's code base, then you want to submit your answer with a code snippet (just several lines) to the question you've found before to help others too. But wait: the company's software is closed source, and you worked on it on the clock. So does this mean I shouldn't post the answer neither at work nor at home to that question in the rest of my life, because I solved it at work, and the company owns that piece of code?

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  • Exchange 2003: Fresh install, couple noob questions.

    - by Eli
    Hi All, Thanks for reading! I have a small network set up for a local office here, and have a fresh install of Exchange 2003 on our sole-server PDC. The network uses one domain, call it ourdomain.net, which is DNSed locally, but not DNSed for the actual domain, so ourdomain.net works from within the network, but from outside, it's just pointed to some domain parking. I have a completely different domain, call it emaildomain.com, which is currently setup for our website and email, which is hosted with a standard hosting company. We've been using a combination of Thunderbird and Outlook (with local .pst files) for email. I've been asked to setup Exchange to work with our email, but am not familiar with it. The install seems to have gone just fine. The question is: How do I get email from a domain outside our network to work with the exchange server? Do I need to move the email for that domain to point to our local server (I so hope not!), or can I just set exchange so somehow slurp mail from the existing mailboxes on our host for that domain's mail? Or are there better ideas I don't know to ask for? Any help very appreciated - thanks!

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  • Problem with MS DTC on SQL2008 win server 2k8 with linked server from sql2000 win server 2k

    - by user31648
    Hi, We have migrated our db from sql2000 win server 2k to sql2008 win server 2k8. We have linked server from sql2000 win server 2k. By our opinion the problem is with DTC and we have made a lot of setting that we found as solution for our problem, but still the problem exist. There is no any error or worning or information niether in the sql log nor in win event viewer. The application is hanging out and at the end the time out exception is shown. What we have done till now: Enable Network DTC Access with inbound and outbound with No Authentication Required on win 2k8 We have opened RPC dynamic port allocation through registry on 2k and 2k8 We have entered subkey TurnOffRpcSecurity in the registry HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\MSDTC and made it enable on 2k and 2k8 We have added exception for DTC in firewall for all entities What we have notice that when we restart SQL service and make the first try for our transaction the following is shown: "Attempting to initialize Microsoft Distributed Transaction Coordinator (MS DTC). This is an informational message only. No user action is required." and after it: "Recovery of any in-doubt distributed transactions involving Microsoft Distributed Transaction Coordinator (MS DTC) has completed. This is an informational message only. No user action is required." Does someone have any idea what else can be done in order to solve the problem? Thanks in advance. Regards, Snezana

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  • External DNS and IIS Webserver requirement for Outlook Anywhere 2007 ?

    - by Albert Widjaja
    Hi, I just would like some clarification about which External hostname / DNS entries that I need to publish in my external facing DNS server to enable Outlook Anywhere on my Exchange Server 2007 for external user: ExCAS01.domain.com - Exchange CAS A Record Autodiscover.domain.com - Autodiscover CNAME to the CAS Server above _autodiscover._tcp.domain.com - SRV type record and do I have to expect anything by typing this address in bowser "https://autodiscover.domain.com/AutoDiscover/AutoDiscover.xml" ? because i get request time out at the moment. here are the error log from https://testexchangeconnectivity.com: Host Excas01.domain.com couldn't be resolved in DNS Exception details: Message: The requested name is valid, but no data of the requested type was found Type: System.Net.Sockets.SocketException Stack trace: at System.Net.Dns.GetAddrInfo(String name) at System.Net.Dns.InternalGetHostByName(String hostName, Boolean includeIPv6) at System.Net.Dns.GetHostAddresses(String hostNameOrAddress) at Microsoft.Exchange.Tools.ExRca.Tests.ResolveHostTest.PerformTestReally() Host autodiscover.domain.com couldn't be resolved in DNS Exception details: Message: The requested name is valid, but no data of the requested type was found Type: System.Net.Sockets.SocketException Stack trace: at System.Net.Dns.GetAddrInfo(String name) at System.Net.Dns.InternalGetHostByName(String hostName, Boolean includeIPv6) at System.Net.Dns.GetHostAddresses(String hostNameOrAddress) at Microsoft.Exchange.Tools.ExRca.Tests.ResolveHostTest.PerformTestReally() Attempting to locate SRV record _autodiscover._tcp.domain.com in DNS. The Autodiscover SRV record wasn't found in DNS.

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  • Migrating from "partial" Exchange 2003 to full Exchange 2003 usability

    - by TheCleaner
    I have a client that is using Exchange 2003 on SBS 2003 R2, but only for calendar sharing and contacts sharing. Their email is still coming to their clients via a POP3 account on each client's Outlook. I'd like to move them over to using Exchange for both email and the other things they are utilizing it for now. Can you folks guide me in the right direction? The setup: external domain is akin to domain.com (and is where they get their POP3 email from now) internal domain is akin to domain.local only simple hardware firewall (no ISA) static external IP is available to use My "assumptions": Setup SMTP default connector in Exchange for their existing external domain Have their existing email backed up to PST files (just in case) Setup the new MX records to point domain.com to the static external IP I'm a little confused how I'm going to setup their existing Exchange accounts with the proper SMTP address though. Right now it is just [email protected]. Do I just need to modify or create a new recipient policy? Are there other steps involved that I'm missing? Anyone with a walkthrough or even a basic "steps" is fine. I'm fairly used to Exchange 03, but I've been on Exchange 07 for a while now so going back is the weird part...plus I don't know what issues Exchange 03 on SBS has versus the normal "version". Thanks for all the help!

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