IMPORTANT:
When i run this:
perl /var/www/ispman/bin/ispman.createMailbox -h sentinel.mydomain.tld
user@mydomain.tld

i get the error above.

But when i run:
perl /var/www/ispman/bin/ispman.createMailbox -h sentinel.mydomain.tld
user_mydomain_tld
then mailbox is creaetd successfully. How to workaround this problem?