Hello helpful server folks,

I'm messing with iRedMail. I've mostly been successful, I think I have an SMTP problem.

I have changed RoundCube (webmail) to use BrightHouse's, my ISP's, SMTP server for outgoing. It works fine, I click send and poof, I have gmail. I can reply from gmail to my email server, and it works. It took 10 hours for the email to show up, which is a different problem, I think, but it does work.

But when I send from my server TO my own server, my ISP's Postmaster account sends me a cryptic blurb. I just got off the phone with them, and they say it "should work", and that they can't reach my pop3 server. (pop3, pop3s, imap, and imaps are all open on my router and forwarded to the server, I'm not sure what I need, I'm just covering my bases...)

pop3 and/or imap as external interfaces are just formalities, I really just want webmail to work.

Roundcube only takes one SMTP server in its configs. How can I configure Postfix to relay / forward emails to my ISP's SMTP, while taking messages bound for my own domain and processing them? Since my ISP won't let me "bounce" my emails off of it.

Maybe I'm vastly misunderstanding how e-mail works in general: To receive mail, I should only need port 25, SMTP, open to the internet, correct? Should I be concerned about some authentication failure from the outside to my relay? (My relay requires user/pass to use, my ISP's requires none.)