Well, I guess by using IP Tables Bill the source port for outgoing connections will be 26 instead of 25. Though the question stands has the OP spoken to the ISP and confirm the situation
Except for the fact you've already said how he should change the outbound relay port, using IPtables won't make any difference - unless I'm asking the usual dumb questions.
Anyway, if mail can be sent via Thunderbird using port 25 then it should work for a mail server using port 25, yes? The only problem is if the ISP requires the use of one of the submission ports such as 587 rather than 25.
Indeed, and that can be sorted by modifying the zmprov command.
> If I configure the Thunderbird to use directly my ISP SMTP (with no authentication nor security) it works!
> But... When I configure in Zimbra admin to relay at the same SMTP is does not!
Somehow i am not convinced that your ISP allows you to relay the mails, but if i trust you and they do, is it IP based relaying they did? Is it that your server IP is in different IP than what your ISP assigns ?
Outgoing SMTP Authentication
I'm having problems, how can I disable the command through command line?
zmprov ms server.domain.com zimbraMtaRelayHost external.relay.com:#
Web Gui does not allow me to change that value.
Good it works now :-)
I'm having the followed message:
SASL authentication failed; cannot authenticate to server smtp.myisp.net[213.xxx.xx.xx]: generic failure