We've seen an obscure problem for one of our servers running on 10.6.4 (Mac OS X Snow Leopard Server) which was upgraded from 10.5. When attempting to implement the iCal Email Invitations function, I found that all of the usual tricks didn't work. The invitations would be sent out, but when the other user attempted to respond, the mail server on the Snow Leopard Server would immediately bounce the message.
The sender would get a bounce back email from their mail server with an error something like:
Failed to deliver to 'com.apple.calendarserver+b2624c28-c913-4bb0-b539-999999999999@domain.com'
SMTP module(domain domain.com) reports:
host domain.com says:
550 5.1.1 <com.apple.calendarserver+b2624c28-c913-4bb0-b539-999999999999@domain.com>: Recipient address rejected: User unknown in local recipient table
In the SMTP logs on the server (/var/log/mail.log), you'd see an equivalent error:
<com.apple.calendarserver+b2624c28-c913-4bb0-b539-999999999999@domain.com>: Recipient address rejected: User unknown in local recipient table
Mail was obviously getting to the server, so I knew my port mapping and mail server setup was correct, but the mail server was rejecting it. In addition, if I sent an email to com.apple.calendarserver@domain.com - without the "+stuff" extension, no error would show up.
We had seen a very similar behavior with emails being sent to a Communigate Server a few months ago, and that issue was related to Communigate's handling of the "user+extension@domain.com" format. However, I knew that 10.6 Server's mail server (postfix) was configured by default to handle this properly, because I'd seen this work on other 10.6 servers.
Still, I hunted around using this as a clue And this is what I found:
If you edit the file "/etc/postfix/mail.cf" (use your terminal text editor of choice and prefix it with "sudo") to get write access, then you can find this around line 399:
recipient_delimiter = +
It looks like that when postfix is upgraded from 10.5 to 10.6, sometimes this line is commented out (with a "#" in front) and not updated properly. So if you see:
#recipient_delimiter = +
Simply remove the "#," and restart the mail service. Then those error messages will disappear.
We hope that this helps anyone else who runs into the same problem. I found that Googling that error message and "iCal Server" came up with nothing useful, so I'm not sure if we're the only ones to see this issue. Hopefully so, because it's a tough one to track down (at least without this post).
