SMTP relayhost

[hede]

Am Sat, 08 Mar 2014 17:53:23 GMT schrieb <simon at simonforsell.se>:

> Company policy only to use ISP smtp...even for local delivery...

Ah, ok, that's really a wired thing. But should be possible with postfix. 

For example, Setting all local destinations to empty strings:

mydestination =
relayhost = [the.relay.host]
transport_maps = 
virtual_mailbox_domains = 

... this will forward all mail to the relay host. (as seen at [1]) 
But all incoming mail for your users will also be forwarded right back to the smarthost. Doh! No good. 

Possible Solution: If all your smtp-clients connect to the submission-port (587) for sending mail and incoming mail is via port 25 (smtp), then the following should be possible:

Leave the configuration of port 25 as it is now and reconfigure port 587 with those empty local destinations. That should do the trick. I think this should be possible via the "submission" configuration in master.cf. Maybe it's possible to use "-o mydestination=''" etc. in it. I never tried that. Maybe you want to give it a try.

AFAIK in the default kolab configuration incoming mails via smtp (port 25) are not allowed to have foreign addresses and login/auth is disabled. Thus all clients which are able to send mail to the internet should already be using port 587. (For me that's the case, but I do not know if it's the default. It's not a postfix-default, which allows using port 25 as the incoming port for local clients.)

regards
hede

[1] http://postfix.1071664.n5.nabble.com/How-to-relay-ALL-mail-to-relayhost-td4788.html)