When I compose a new message, I click send and even on one word subject message it will take anywhere from 2-5 minutes for the message to get passed to Postfix. I can tell this because I am tailling the maillog for Postfix and wait for it to show up. Once it hits Postfix it goes right out. All other apsects of Roundcube are responsive, all folders load quickly, messages are received quickly as well. I'm using Dovecot and Postfix for IMAP and SMTP and followed the directions here http://www.rosehosting.com/blog/mailserver-with-virtual-users-and-domains-using-postfix-and-dovecot-on-a-centos-6-vps/ to set it up. Sending messages was snappy at first but now I have the lag and there is literally nothing in the mail queue and again it's not even being submitted to the queue based on what I'm seeing in the maillog.
There is no Apache errors and no errors logged in the roundcube logs either.
Ok I resolved this. Not sure what the issue was but I disabled spell checking by unchecking in Settings. Can someone tell me how to get spell check working properly?
http://trac.roundcube.net/wiki/Howto_Config/Aspell
Thanks for posting your solution to this. I was having the very same issue, and had already spent hours trying to figure it out.
My problem also involved Nginx killing the connection, timing out after 60s and reporting back as 503. This confuses the mail composer, which then thinks it remained unsent.