After spending a lot of time reading and playing with the config files, still no luck: in Roundcube it still says netrin@127.0.0.1 instead of netrin@mydomain.com and I cannot send or receive mail. Sorry to bump, but any suggestions?
Found some info in/var/mail/mail.log that looks strange--does this help us understand the problem at all?
Aug 12 14:36:01 mail postfix/pipe[6610]: 351117F8AF: to=<postmaster@mydomain.net>, relay=dovecot, delay=13071, delays=13069/1.1/0/0.45, dsn=4.3.0, status=deferred (temporary failure)
Aug 12 14:36:01 mail postfix/smtp[6599]: connect to 127.0.0.1[127.0.0.1]:10024: Connection refused
Aug 12 14:36:01 mail postfix/smtp[6607]: connect to 127.0.0.1[127.0.0.1]:10024: Connection refused
Aug 12 14:36:01 mail postfix/smtp[6599]: 958E07F8BC: to=<root@mail.mydomain.net>, relay=none, delay=9359, delays=9357/1.5/0.12/0, dsn=4.4.1, status=deferred (connect to 127.0.0.1[127.0.0.1]:10024: Connection refused)
Aug 12 14:36:01 mail postfix/smtp[6607]: E42437F8AE: to=<root@mail.mydomain.net>, relay=none, delay=12959, delays=12958/1.5/0.12/0, dsn=4.4.1, status=deferred (connect to 127.0.0.1[127.0.0.1]:10024: Connection refused)
Aug 12 14:36:01 mail postfix/error[6619]: 495AD7FB21: to=<root@mail.mydomain.net>, relay=none, delay=2159, delays=2158/1.7/0/0.03, dsn=4.4.1, status=deferred (delivery temporarily suspended: connect to 127.0.0.1[127.0.0.1]:10024: Connection refused)
Aug 12 14:39:04 mail postfix/pickup[5757]: 795967FB2E: uid=0 from=<root>
Aug 12 14:39:04 mail postfix/cleanup[6643]: 795967FB2E: message-id=<20140812183904.795967FB2E@mail.mydomain.net>
Aug 12 14:39:04 mail postfix/qmgr[3861]: 795967FB2E: from=<root@mail.mydomain.net>, size=830, nrcpt=1 (queue active)
Aug 12 14:39:04 mail postfix/error[6645]: 795967FB2E: to=<root@mail.mydomain.net>, relay=none, delay=0.38, delays=0.29/0.03/0/0.05, dsn=4.4.1, status=deferred (delivery temporarily suspended: connect to 127.0.0.1[127.0.0.1]:10024: Connection refused)
Aug 12 14:39:21 mail postfix/scache[6618]: statistics: start interval Aug 12 14:36:01
Aug 12 14:39:21 mail postfix/scache[6618]: statistics: domain lookup hits=0 miss=2 success=0%
Aug 12 14:39:21 mail postfix/scache[6618]: statistics: address lookup hits=0 miss=2 success=0%
Aug 12 14:40:02 mail postfix/pickup[5757]: 233D280391: uid=109 from=<smmsp>
Aug 12 14:40:02 mail postfix/cleanup[6643]: 233D280391: message-id=<20140812184002.233D280391@mail.mydomain.net>
Aug 12 14:40:02 mail postfix/qmgr[3861]: 233D280391: from=<smmsp@mail.mydomain.net>, size=696, nrcpt=1 (queue active)
Aug 12 14:40:02 mail postfix/error[6645]: 233D280391: to=<root@mail.mydomain.net>, relay=none, delay=0.27, delays=0.21/0/0/0.05, dsn=4.4.1, status=deferred (delivery temporarily suspended: connect to 127.0.0.1[127.0.0.1]:10024: Connection refused)
Aug 12 14:45:58 mail postfix/qmgr[3861]: 840DD7F8B2: from=<>, size=2892, nrcpt=1 (queue active)
Aug 12 14:45:58 mail postfix/qmgr[3861]: 795967FB2E: from=<root@mail.mydomain.net>, size=830, nrcpt=1 (queue active)
Aug 12 14:45:58 mail postfix/qmgr[3861]: 95D657FB2B: from=<>, size=2558, nrcpt=1 (queue active)
Aug 12 14:45:58 mail postfix/qmgr[3861]: 9DC1D7FB0F: from=<root@mail.mydomain.net>, size=830, nrcpt=1 (queue active)
Aug 12 14:45:58 mail postfix/qmgr[3861]: C01007F8B1: from=<root@mail.mydomain.net>, size=830, nrcpt=1 (queue active)
Aug 12 14:45:58 mail postfix/qmgr[3861]: CB7697F8A8: from=<smmsp@mail.mydomain.net>, size=696, nrcpt=1 (queue active)
Aug 12 14:45:58 mail postfix/qmgr[3861]: 233D280391: from=<smmsp@mail.mydomain.net>, size=696, nrcpt=1 (queue active)
Aug 12 14:45:58 mail postfix/qmgr[3861]: 37BF67FB2C: from=<root@mail.mydomain.net>, size=830, nrcpt=1 (queue active)
Aug 12 14:45:59 mail postfix/smtp[7114]: connect to 127.0.0.1[127.0.0.1]:10024: Connection refused
Aug 12 14:45:59 mail postfix/smtp[7114]: 795967FB2E: to=<root@mail.mydomain.net>, relay=none, delay=415, delays=414/0.24/0/0, dsn=4.4.1, status=deferred (connect to 127.0.0.1[127.0.0.1]:10024: Connection refused)
Aug 12 14:45:59 mail postfix/smtp[7117]: connect to 127.0.0.1[127.0.0.1]:10024: Connection refused
Aug 12 14:45:59 mail postfix/smtp[7117]: 9DC1D7FB0F: to=<root@mail.mydomain.net>, relay=none, delay=9415, delays=9414/0.47/0.01/0, dsn=4.4.1, status=deferred (connect to 127.0.0.1[127.0.0.1]:10024: Connection refused)
Aug 12 14:45:59 mail postfix/local[7115]: 95D657FB2B: to=<smmsp@mail.mydomain.net>, relay=local, delay=2400, delays=2399/0.32/0/0.38, dsn=4.3.0, status=deferred (temporary failure. Command output: Can't open log file /var/log/dovecot-sieve.log: Permission denied )
Aug 12 14:45:59 mail postfix/pipe[7113]: 840DD7F8B2: to=<postmaster@mydomain.net>, relay=dovecot, delay=17269, delays=17268/0.44/0/0.68, dsn=4.3.0, status=deferred (temporary failure)
Aug 12 14:45:59 mail postfix/qmgr[3861]: 840DD7F8B2: from=<>, status=expired, returned to sender
Aug 12 14:45:59 mail postfix/qmgr[3861]: 840DD7F8B2: removed
Aug 12 14:45:59 mail postfix/smtp[7114]: connect to 127.0.0.1[127.0.0.1]:10024: Connection refused
Aug 12 14:45:59 mail postfix/smtp[7117]: connect to 127.0.0.1[127.0.0.1]:10024: Connection refused
Aug 12 14:45:59 mail postfix/smtp[7114]: C01007F8B1: to=<root@mail.mydomain.net>, relay=none, delay=13016, delays=13015/0.61/0.17/0, dsn=4.4.1, status=deferred (connect to 127.0.0.1[127.0.0.1]:10024: Connection refused)
Aug 12 14:45:59 mail postfix/smtp[7117]: CB7697F8A8: to=<root@mail.mydomain.net>, relay=none, delay=17158, delays=17157/0.62/0.16/0, dsn=4.4.1, status=deferred (connect to 127.0.0.1[127.0.0.1]:10024: Connection refused)
Aug 12 14:45:59 mail postfix/qmgr[3861]: CB7697F8A8: from=<smmsp@mail.mydomain.net>, status=expired, returned to sender
Aug 12 14:45:59 mail postfix/error[7125]: 233D280391: to=<root@mail.mydomain.net>, relay=none, delay=358, delays=357/0.87/0/0.1, dsn=4.4.1, status=deferred (delivery temporarily suspended: connect to 127.0.0.1[127.0.0.1]:10024: Connection refused)
Aug 12 14:45:59 mail postfix/error[7127]: 37BF67FB2C: to=<root@mail.mydomain.net>, relay=none, delay=2216, delays=2215/0.92/0/0.06, dsn=4.4.1, status=deferred (delivery temporarily suspended: connect to 127.0.0.1[127.0.0.1]:10024: Connection refused)
Aug 12 14:45:59 mail postfix/cleanup[7126]: E41247F8B2: message-id=<20140812184559.E41247F8B2@mail.mydomain.net>
Aug 12 14:46:00 mail postfix/qmgr[3861]: E41247F8B2: from=<>, size=2558, nrcpt=1 (queue active)
Aug 12 14:46:00 mail postfix/bounce[7118]: CB7697F8A8: sender non-delivery notification: E41247F8B2
Aug 12 14:46:00 mail postfix/qmgr[3861]: CB7697F8A8: removed
Aug 12 14:46:00 mail postfix/local[7115]: E41247F8B2: to=<smmsp@mail.mydomain.net>, relay=local, delay=0.5, delays=0.33/0/0/0.17, dsn=4.3.0, status=deferred (temporary failure. Command output: Can't open log file /var/log/dovecot-sieve.log: Permission denied )
Not sure if this helps, but I also noticed that when logged in as postmaster, a few root e-mails appeared and were from root@mail.mydomain.com . Is this typical or should it be from root@mydomain.com instead?