MacOS – SMTP Issues with Mountain Lion 10.8

BACKGROUND

1. I upgraded from 10.7 to 10.8 on 7/28/12
2. I upgraded Xcode from 4.4 to 4.4.1 on 8/8/12

PROBLEM

• On 8/9/12, on my MacBook Air, Mail.app refuses to connect to the SMTP service on a server that I frequently use. Mail.app reliably connects to the IMAP and WWW services running on the exact same server. Mail.app also reliably connects to 4 or 5 other SMTP servers.

SETTINGS

1. Incoming Mail is set to use IMAP on 993 with SSL. No problems with incoming mail.
2. Outgoing Mail is set to use the default ports, with SSL and Password authentication.

EFFORTS TO RESOLVE THE PROBLEM

1. I can telnet to the server on port 587 with no issue. The server responds as it should.
2. I can ping the server and connect to it via SSH or WWW.
3. My iPhone and iPad with the exact same SMTP settings are able to, from the same WiFi network, send mail without issue.
4. The same problem happens if I use the server's public IP or its domain.
5. I experience this on my network at work and when connected through a VPN to another network.
6. I have deleted and recreated the SMTP server in Mail.app with no success.
7. I have deleted and reinstalled the certificates associated with the server with no success.
8. I tried to create a new IMAP and SMTP account for the same server using another name and password. Upon setup, IMAP was found and connected immediately, but the SMTP server was never found.
9. Using Sparrow, I tried to add an account on the server and also did not get past the SMTP portion.
10. Connection doctor shows NOTHING as far as attempts to reach the server for SMTP. All IMAP attempts are logged and attempts to reach the other SMTP servers appear as they should. But, there is nothing showing for attempts to reach the SMTP service on the server in question.
11. In my SMTP server settings, I tried manually adding 587 both with SSL and without without any success. My mail server only accepts on 587.
12. Restarted Mail, restarted MacBook Air, flushed DNS entries.
13. Dragged the Mail and Mail Downloads Folders out of ~/Library and tried recreating the account. Again, it connected to IMAP fine, but stalled when trying to connect to the SMTP server.