Thank you Steffen Kaiser. I enabled the auth_debug and saw this error for permissions:
Aug 22 13:41:44 managesieve($u): Error: sieve-storage: Creating symlink() /home/$u/.dovecot.sieve to sieve/Out of office.sieve failed: Permission denied The user's home directory was owned by root. Can not explain it why it was so. Thanks again! > On Wed, 21 Aug 2013, Joe Lourenco wrote: > > > roundcube: S: NO (TRYLATER) "Internal error occured. Refer to server log > > for more information. [2013-08-21 19:01:13]" > > > Nothing is showing up on the server log. > > Check out Dovecot's error log and search for that timestamp of the > message, it is there - unless, say, an out of disk error prevented the > logging. >