I am running nginx 1.1.19 on an Ubuntu 12.04.4 64but server.

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.

My nginx error.log shows the following:
*5 upstream sent invalid response: "* CAPABILITY IMAP4rev1 UNSELECT IDLE NAMESPACE QUOTA ID XLIST CHILDREN X-GM-EXT-1 UIDPLUS COMPRESS=DEFLATE ENABLE MOVE CONDSTORE ESEARCH
a1 OK test@example.com Test User authenticated (Success)" while reading response from upstream,...

It appears to not like google's CAPABILITY line. Is it too long? Any suggestions?

Other connections through nginx/stunnel to exchange work just fine.