Steps to reproduce:
1) Deploy the Mail EE portlet version 1.0.0 on a vanilla Liferay 6.1.20 (No portal-ext.properties)
2) Add the Mail portlet to the Welcome page
3) Set up a test gmail account (IMAP enabled) successfully!
4) Click on the "Compose Email" function
a) Fill out the following inputs: To,Subject,Body
b) Click on save button
c) Choose an attachment
d) Save again
5) Attempt to send an email message
Observed behavior: Now you get the red warning message: "Unable to send message." and also got some exceptions in the log file. Attached: "liferay.2013-04-29.log"
Another try, I've got these exceptions: "liferay.2013-04-30.log" with another account (custom one in my case)
These accounts and the above functions works correctly if I add these accounts beside a specified one.