I too, am getting this problem. I get an Error 500 on the popup message box. However, I have tested several other mail programs and none of them require SSL.
Email sending appears to be ok, however, email receipt appears to be problem. I even scoured your forums for a fix and came across one post that suggested a process for adding a POP3_port to the database and several files. This did not work and I was forced to revert to my original file and database structure.
From start to finish, here's what I get...
I log in and when the screen comes up, I immediately get a "Method not supported" message. No other information can be found (unless you can point me to a more verbose error log). Nothing is missing on the screen and all of the buttons and tabs are working.
I click on EMAIL (Beta) and "check mail". It pauses for a moment and tells me that I have an Internal Server Error 500. If I go and look in the mailbox via squirrelmail or something, there is an item in the box, unread and untouched. If I were to delete that message, I could "check mail" from inside OpenGoo and it would report no errors, with no emails picked up. However, if there is a message in the box, it dies.
Sending mail - I have NO problems with.
My server uses standard ports 110 for POP3 and 25 for SMTP. I've tried addressing the "mail server" by IP, web domain name as well as localhost to no avail.
I am running CentOS and cPanel.