Sendmail client - how does it know?

[jouell]

Hi,

I understand we do not need sendmail listening on port 25 to send outbound mail w/mail and mailx. How do these mail clients know to use sendmail as the MTA?

If I modify sendmail.cf (I.E to forward all mail to a host) will it really affect mail delivery?

Thanks!
-John

 

[Rhinokiller]

I think a basic example works best here.
If you have a mail client that is set up for POP3, then your client will query the mail server on port 110 and expect to find the POP3 service active and awaiting connection requests. If everything is configured properly the mail server will deliver mail to the mail client.
If the same mail client needs to send mail to the mail server it will contact the mail server using port 25 (smtp) and expect to find the smtp/esmtp service active and ready to process client requests.
It doesn't really matter what MTA you're using as long as you configure that MTA to act as the local mailer for your mail system. You don't have to use sendmail, you can use whatever you want.

Cogito Ergo Sum - Non Compos Mentis

 

[jouell]

Ok but why does mailx on hostA hand off to the sendmail process on HostA? I have not defined an smtp server anywhere.

 

[jad]

mailx == sendmail (usually) they're usually links (hard or soft) to the same program ... and it is affected by what $0 is set to ...

Although i may be wrong

 

[jouell]

hmm i think you are right jad. I bet mailx could not send to any other smtp server unless it was linked in somehow....