New ZCS installs already are configured to listen on port 587; its the "submission" port in master.cf.
Originally Posted by wariola
Port 465 comes from a never-ratified RFC and its use should be avoided if possible. Hard to do I know with older versions of Outlook, but it's still there in Zimbra so you should be OK.
This is a common problem with traveling laptop users whose home or hotel ISP blocks port 25, where the user doesn't want (or doesn't know how) to change their Outlook settings every time they change locations.
If you see the following in /opt/zimbra/postfix/conf/master.cf.in you should be OK for now and upgrades should not change anything:
Now, if you are saying that your ISP is blocking port 25 outbound from your Zimbra host, that's a different scenario, and I would just configure Zimbra to use your ISP's smtp server as a Relay Host. This is configured in the Admin Console.
# Postfix master process configuration file. For details on the format
# of the file, see the Postfix master(5) manual page.
# service type private unpriv chroot wakeup maxproc command + args
# (yes) (yes) (yes) (never) (100)
smtp inet n - n - - smtpd
465 inet n - n - - smtpd
submission inet n - n - - smtpd
Hope that helps,