2018-01-02 01:40:59 imap(info@saic.it): Fatal: master: service(imap): child 18780 killed with signal 6 (core dumps disabled)
2018-01-02 01:40:59 imap(info@saic.it): Error: /var/vmail/saic.it/info/Maildir/dovecot.index: modseq_hdr.log_offset too large
2018-01-02 01:40:59 imap(info@saic.it): Error: /var/vmail/saic.it/info/Maildir/dovecot.index: modseq_hdr.log_offset too large
2018-01-02 01:40:59 imap(info@saic.it): Panic: file mail-transaction-log-file.c: line 1148 (mail_transaction_log_file_get_highest_modseq_at): assertion fa
iled: (offset <= file->sync_offset)
HOW TO SOLVE
find /var/vmail/saic.it/info/Maildir/ -name "dovecot*" -delete
Restart Postfix & Dovecot (to rebuild the dovecot files):
$ service dovecot restart $ service postfix restart
I think the cause is the presence of a virus in some emails attachment.