I seem having the same problem.
I'm not sure if the messages are been down loaded or not but they are not delivered to my local mailboxes in SOGo:
Copy of mail.log below any help would be appreciated.
Feb 25 11:39:19 Zentyal postfix/master[3260]: terminating on signal 15
Feb 25 11:39:19 Zentyal postfix[4706]: Postfix is running with backwards-compatible default settings
Feb 25 11:39:19 Zentyal postfix[4706]: See
http://www.postfix.org/COMPATIBILITY_README.html for details
Feb 25 11:39:19 Zentyal postfix[4706]: To disable backwards compatibility use "postconf compatibility_level=2" and "postfix reload"
Feb 25 11:39:20 Zentyal postfix/master[4743]: daemon started -- version 3.1.0, configuration /etc/postfix
Feb 25 11:39:20 Zentyal dovecot: master: Warning: Killed with signal 15 (by pid=4765 uid=0 code=kill)
Feb 25 11:39:20 Zentyal dovecot: master: Dovecot v2.2.22 (fe789d2) starting up for pop3, imap, sieve (core dumps disabled)
Feb 25 11:39:20 Zentyal fetchmail[2959]: terminated with signal 15
Feb 25 11:39:21 Zentyal fetchmail[4820]: starting fetchmail 6.3.26 daemon
Feb 25 11:39:21 Zentyal fetchmail[4820]: 56 messages (56 seen) for colin@Mydomain at claudio.secure.kualo.net.
Feb 25 11:40:22 Zentyal fetchmail[4820]: 56 messages (56 seen) for colin@Mydomain at claudio.secure.kualo.net.
Feb 25 11:41:22 Zentyal fetchmail[4820]: 56 messages (56 seen) for colin@Mydomain at claudio.secure.kualo.net.
Feb 25 11:42:11 Zentyal dovecot: imap-login: Login: user=<colin@Mydomain>, method=PLAIN, rip=127.0.0.1, lip=127.0.0.1, mpid=5480, secured, session=<RN08VllJ3MR/AAAB>
Feb 25 11:42:11 Zentyal dovecot: imap(colin@Mydomain): Logged out in=127 out=1248
Feb 25 11:42:12 Zentyal dovecot: imap-login: Login: user=<colin@Mydomain>, method=PLAIN, rip=127.0.0.1, lip=127.0.0.1, mpid=5486, secured, session=<utlHVllJ4sR/AAAB>
Feb 25 11:42:12 Zentyal dovecot: imap-login: Login: user=<colin@Mydomain>, method=PLAIN, rip=127.0.0.1, lip=127.0.0.1, mpid=5487, secured, session=<+SdIVllJ5sR/AAAB>
Feb 25 11:42:12 Zentyal dovecot: imap(colin@Mydomain): Logged out in=143 out=1353
Feb 25 11:42:12 Zentyal dovecot: imap(colin@Mydomain): Logged out in=216 out=1442
Feb 25 11:42:23 Zentyal fetchmail[4820]: 56 messages (56 seen) for colin@Mydomain at claudio.secure.kualo.net.