I've been struggling with this on and off for a while now. Upon attempting to install Dovecot on Ubuntu 17.04 I get the following errors
Selecting previously unselected package dovecot-imapd. (Reading database ... 243684 files and directories currently installed.) Preparing to unpack .../dovecot-imapd_1%3a2.2.27-2ubuntu2_amd64.deb ... Unpacking dovecot-imapd (1:2.2.27-2ubuntu2) ... Processing triggers for dovecot-core (1:2.2.27-2ubuntu2) ... Processing triggers for ufw (0.35-4) ... Setting up dovecot-imapd (1:2.2.27-2ubuntu2) ... Creating config file /etc/dovecot/conf.d/20-imap.conf with new version Processing triggers for dovecot-core (1:2.2.27-2ubuntu2) ... Job for dovecot.service failed because the control process exited with error code. See "systemctl status dovecot.service" and "journalctl -xe" for details. invoke-rc.d: initscript dovecot, action "restart" failed. dovecot.service - Dovecot IMAP/POP3 email server Loaded: loaded (/lib/systemd/system/dovecot.service; enabled; vendor preset: enabled) Active: failed (Result: exit-code) since Thu 2017-10-05 14:08:56 BST; 17ms ago Docs: man:dovecot(1) http://wiki2.dovecot.org/ Process: 8880 ExecStop=/usr/bin/doveadm stop (code=exited, status=0/SUCCESS) Process: 8885 ExecStart=/usr/sbin/dovecot (code=exited, status=89) Main PID: 8729 (code=exited, status=0/SUCCESS)
Oct 05 14:08:56 ash systemd[1]: Starting Dovecot IMAP/POP3 email server... Oct 05 14:08:56 ash dovecot[8885]: Error: socket() failed: Address family n…ocol Oct 05 14:08:56 ash dovecot[8885]: Error: service(imap-login): listen(::, 1…ocol Oct 05 14:08:56 ash dovecot[8885]: master: Error: socket() failed: Address …ocol Oct 05 14:08:56 ash dovecot[8885]: Fatal: Failed to start listeners Oct 05 14:08:56 ash systemd[1]: dovecot.service: Control process exited, co…s=89 Oct 05 14:08:56 ash systemd[1]: Failed to start Dovecot IMAP/POP3 email server. Oct 05 14:08:56 ash systemd[1]: dovecot.service: Unit entered failed state. Oct 05 14:08:56 ash systemd[1]: dovecot.service: Failed with result 'exit-code'. Hint: Some lines were ellipsized, use -l to show in full. dpkg: error processing package dovecot-core (--configure): subprocess installed post-installation script returned error exit status 1 (and more)
Apologies for any wrapping due to long lines in the above output.