Well I've found this related article:
http://virer.net/info/ol-autodiscover/index.html
Tried it and it seems to be working until the last step... issue with the authentication.
So I saw this in the log files:
2013-12-22 14:22:59 SMTP protocol synchronization error (input sent without waiting for greeting): rejected connection from H=xxx [xxx.xxx.xxx.xxx] input="\026\003\003\001K\001"
2013-12-22 14:22:59 SMTP protocol synchronization error (input sent without waiting for greeting): rejected connection from H=xxx [xxx.xxx.xxx.xxx] input="\026\003\003\001F\001"
Dec 22 14:23:42 WEBSRV01 dovecot[1150]: auth-worker(24081): shadow(webmaster,xxx.xxx.xxx.xxx): unknown user
Dec 22 14:23:42 WEBSRV01 dovecot[1150]: auth: Error: passwd-file(webmaster,xxx.xxx.xxx.xxx,<+HqRax/uTgBe4p0g>): stat(/etc/virtual//passwd) failed: No such file or directory
Dec 22 14:23:43 WEBSRV01 dovecot[1150]: auth-worker(24082): shadow(webmaster,xxx.xxx.xxx.xxx): unknown user
Dec 22 14:23:43 WEBSRV01 dovecot[1150]: auth: Error: passwd-file(webmaster,xxx.xxx.xxx.xxx,<+eiRax/uTwBe4p0g>): stat(/etc/virtual//passwd) failed: No such file or directory
Dec 22 14:23:43 WEBSRV01 dovecot[1150]: auth-worker(24083): shadow(webmaster,xxx.xxx.xxx.xxx): unknown user
Dec 22 14:23:43 WEBSRV01 dovecot[1150]: auth: Error: passwd-file(webmaster,xxx.xxx.xxx.xxx,<50WSax/uUABe4p0g>): stat(/etc/virtual//passwd) failed: No such file or directory
Dec 22 14:23:44 WEBSRV01 dovecot[1150]: auth-worker(24081): shadow(
[email protected],xxx.xxx.xxx.xxx): unknown user
Dec 22 14:23:44 WEBSRV01 dovecot[1150]: auth-worker(24081): passwd(
[email protected],xxx.xxx.xxx.xxx): unknown user
Dec 22 14:23:44 WEBSRV01 dovecot[1150]: imap-login: Login: user=<
[email protected]>, method=PLAIN, rip=xxx.xxx.xxx.xxx, lip=xxx.xxx.xxx.xxx, mpid=24084, session=<+HqRax/uTgBe4p0g>
Dec 22 14:23:44 WEBSRV01 dovecot[1150]: imap(
[email protected]): Disconnected: Logged out in=11 out=402
Dec 22 14:23:45 WEBSRV01 dovecot[1150]: auth-worker(24081): shadow(
[email protected],xxx.xxx.xxx.xxx): unknown user
Dec 22 14:23:45 WEBSRV01 dovecot[1150]: pop3-login: Disconnected (auth failed, 1 attempts in 3 secs): user=<webmaster>, method=PLAIN, rip=xxx.xxx.xxx.xxx, lip=xxx.xxx.xxx.xxx, session=<50WSax/uUABe4p0g>
Dec 22 14:23:45 WEBSRV01 dovecot[1150]: auth-worker(24081): passwd(
[email protected],xxx.xxx.xxx.xxx): unknown user
Dec 22 14:23:45 WEBSRV01 dovecot[1150]: imap-login: Login: user=<
[email protected]>, method=PLAIN, rip=xxx.xxx.xxx.xxx, lip=xxx.xxx.xxx.xxx, mpid=24085, session=<+eiRax/uTwBe4p0g>
Dec 22 14:23:45 WEBSRV01 dovecot[1150]: imap(
[email protected]): Disconnected: Logged out in=11 out=402
Dec 22 14:23:45 WEBSRV01 dovecot[1150]: pop3-login: Aborted login (no auth attempts in 0 secs): user=<>, rip=xxx.xxx.xxx.xxx, lip=xxx.xxx.xxx.xxx, session=<WRO7ax/uUgBe4p0g>
Dec 22 14:23:47 WEBSRV01 dovecot[1150]: auth-worker(24081): shadow(webmaster,xxx.xxx.xxx.xxx): unknown user
Dec 22 14:23:47 WEBSRV01 dovecot[1150]: auth: Error: passwd-file(webmaster,xxx.xxx.xxx.xxx,<LZaSax/uUQBe4p0g>): stat(/etc/virtual//passwd) failed: No such file or directory