Thank you. That is what I thought and have implimented. Tracing the problem further, my imap connection successfully authenticates and then gets a "connection closed by foreign host" going through nginx. The pop connection works just fine, but imap fails.

I have nginx configured to enter on port 143 and go out to 127.0.0.1:143 where it goes through stunnel to go to imap.gmail.com:993. If I talk directly to 127.0.0.1:143 (to stunnel) it works. If I talk to nginx, it authenticates, logs correct username, target IP and port, gets the Capability list and registers a successful login to the remote (gmail) imap server and then closes the connection immediately. The following is a transcript of the telnet session:

telnet nginx:143
* OK IMAP4 ready
a1 LOGIN user@example.com password
* CAPABILITY IMAP4rev1 UNSELECT IDLE NAMESPACE QUOTA ID XLIST CHILDREN X-GM-EXT-1 UIDPLUS COMPRESS=DEFLATE ENABLE MOVE CONDSTORE ESEARCH
a1 OK user@example.com first_name Last_name authenticated (Success)
Connection closed by foreign host.

Any suggestions as to what to try next to diagnose this? (Thanks in advance)