Погиб почтой с сигналом 15

Мой Довекот всегда падает примерно через полчаса. /var/log/mail.log ошибок ( /var/log/mail.log ) говорит:

 Sep 24 12:05:07 yetzner dovecot: imap-login: Warning: Killed with signal 15 (by pid=1 uid=0 code=kill) Sep 24 12:05:07 yetzner dovecot: message repeated 2 times: [ imap-login: Warning: Killed with signal 15 (by pid=1 uid=0 code=kill)] Sep 24 12:05:07 yetzner dovecot: auth-worker(32132): Warning: Killed with signal 15 (by pid=1 uid=0 code=kill) Sep 24 12:05:07 yetzner dovecot: imap: Warning: Killed with signal 15 (by pid=1 uid=0 code=kill) Sep 24 12:05:07 yetzner dovecot: imap: Server shutting down. in=150 out=591 Sep 24 12:05:07 yetzner dovecot: imap: Warning: Killed with signal 15 (by pid=1 uid=0 code=kill) Sep 24 12:05:07 yetzner dovecot: imap: Server shutting down. in=889 out=3101 Sep 24 12:05:07 yetzner dovecot: imap: Warning: Killed with signal 15 (by pid=1 uid=0 code=kill) Sep 24 12:05:07 yetzner dovecot: imap: Warning: Killed with signal 15 (by pid=1 uid=0 code=kill) Sep 24 12:05:07 yetzner dovecot: imap: Server shutting down. in=9446 out=201067 Sep 24 12:05:07 yetzner dovecot: imap: Server shutting down. in=10705 out=1969769 Sep 24 12:05:07 yetzner dovecot: imap: Warning: Killed with signal 15 (by pid=1 uid=0 code=kill) Sep 24 12:05:07 yetzner dovecot: imap: Server shutting down. in=10109 out=458737 Sep 24 12:05:07 yetzner dovecot: imap: Warning: Killed with signal 15 (by pid=1 uid=0 code=kill) Sep 24 12:05:07 yetzner dovecot: imap: Server shutting down. in=9041 out=154798 Sep 24 12:05:07 yetzner dovecot: imap: Warning: Killed with signal 15 (by pid=1 uid=0 code=kill) Sep 24 12:05:07 yetzner dovecot: imap: Server shutting down. in=11253 out=462703 

До этого мой почтовый сервер работает хорошо. После этого я должен перезапустить службу dovecot. Что убивает голубь?