I have a VPS server that I would like to get an SSL certificate for, and the CA needs an email address to verify that I own the domain.  The options are: 
[email protected], 
[email protected], 
[email protected], and an address to @whoisguard.com.
The server runs CentOS 5, and all I have set up for email is sendmail.  I don't have POP3 or IMAP.  According to this Wikipedia article on Postmaster, it says that all SMTP servers support postmaster and it cites 
RFC 5321.  Does sendmail conform to this?  I tried sending a test mail to 
[email protected], but I don't know how to receive it on my server.  Do I need to open up any ports?
I haven't gotten a message back saying that my test mail failed to send, so my server must have gotten it.