I have an issue with mail today too. It stopped working this am some time. I understand that there was a thread somewhere in the last few weeks that explained WHY some mail wasn't working. Some accounts were sending WAY TOO MUCH mail.
Here is the error message:
Connecting to mail.mywebsitename.pcriot.com:143 (imap)
Warning: imap_open() [function.imap-open]: Couldn't open stream {mail.mywebsitename.pcriot.com:143/service=imap/notls/novalidate-cert} in /home/mywebsitename/public_html/wp/wp-content/plugins/postie/postieIMAP.php on line 78
Mail Connection Time Out
Common Reasons:
Server Down
Network Issue
Port/Protocol MisMatch
The Server said:Can not authenticate to IMAP server: [CLOSED] IMAP connection broken (authenticate)