transport plesk_virtual failure

Hello,

All the clients in one of my servers Plesk 12.5 can´t receive or send mails. Also webmail with a 500 error.

I check the logs:

Sep 29 18:17:03 server postfix/qmgr[1134]: warning: transport plesk_virtual failure -- see a previous warning/fatal/panic logfile record for the problem description

Any ideas?