Thank you. If the DNS administrator give me an A record then can I sending and receiving emails from the Internet by the current configuration?
On Thursday, October 15, 2020, 08:49:36 PM GMT+3:30, Wietse Venema <wie...@porcupine.org> wrote: Jason Long: > Thank you, but I never got my answer.1- Postfix or Dovecot has any > option about changing default record that a mail server using?2- > Could A record offer MX record in my goal? An SMTP server cannnot tell remote systems what TCP port they should connect to, or what DNS record they should ask for. Wietse > On Wed, Oct 14, 2020 at 10:09 PM, Wietse Venema<wie...@porcupine.org> wrote: > Jaroslaw Rafa: > > Dnia 14.10.2020 o godz. 13:38:12 Wietse Venema pisze: > > > Here's some email basics. > > > > > > 1) You arrange for an MX and/or A record in your DNS zone. You edit > > > the zone file yourself, or you use some provider's application to > > > edit their zone file. > > > > > >? ? example.com? ? ? ? 10 IN? MX? mail.example.com. > > >? ? mail.example.com.? ? ? IN? ? A? 10.0.0.2 > > > > > > 2) SMTP uses destination port 25 for MTA-to-MTA traffic, therefore > > > the port information is not in the DNS. > > > > > > 3) Some remote MTA looks up your MX and/or A record and connects to > > > your Postfix servers on port 25. > > > > I think there's one important thing to add. > > > > If you have a setup as above, then for mail addressed to "u...@example.com", > > the remote MTA checks the MX record for example.com domain, finds out that > > it points to mail.example.com, checks the A record for mail.example.com and > > connects to the IP address found. > > > > However, if the sender addresses the email to "u...@mail.example.com", the A > > record for mail.example.com is sufficient to have mail delivered (assuming > > your Postfix is configured to honor both example.com and mail.example.com > > names as "mydestination"). The MX record for example.com domain is not > > involved in the process, as the domain in the e-mail address is > > mail.example.com and not example.com. > > > > If there is another server within the example.com domain and it has it's own > > independent Postfix instance, if you add A record for that server to the > > zone file, you can send mail directly to it: > > > >? ? othermail.example.com.? ? ? IN? ? A? 10.0.0.4 > > > > Then messages addressed to "u...@othermail.example.com" will go to that > > other server, while messages to "u...@example.com" will still go to > > mail.example.com. > > > > You should not try to add another MX record for example.com domain pointing > > to othermail.example.com, because if you do this, and email service on both > > servers is not synchronized (which is not quite easy to do), the remote MTA > > sending mail to "u...@example.com" will connect randomly to mail.example.com > > or othermail.example.com, so the message will end up at random on one or the > > other server (but never on both). > > Except when the MX records have different preferences: > > ? ? example.com? ? ? ? 10 IN? MX? mail.example.com. > ? ? example.com? ? ? ? 20 IN? MX? othermail.example.com. > ? ? mail.example.com.? ? ? IN? ? A? 10.0.0.2 > othermail.example.com.? ? ? IN? ? A? 10.0.0.4 > > Then, Postfix on othermail.example.com will forward u...@example.com > to the primary MX host mail.example.com (assuming that mydestination > is configured correctly, i.e. it does not contain example.com). > > ??? Wietse > >
