The following section covers more involved topics such as mail configuration and
setting up mail for your entire domain.
Out of the box, you should be able to send email to external hosts as long as you have
set up /etc/resolv.conf or are running your own name server. If
you would like to have mail for your host delivered to the MTA (e.g., sendmail) on your own FreeBSD host, there are two methods:
-
Run your own name server and have your own domain. For example, FreeBSD.org
-
Get mail delivered directly to your host. This is done by delivering mail directly to
the current DNS name for your machine. For example, example.FreeBSD.org.
Regardless of which of the above you choose, in order to have mail delivered directly
to your host, it must have a permanent static IP address (not a dynamic address, as with
most PPP dial-up configurations). If you are behind a firewall, it must pass SMTP traffic
on to you. If you want to receive mail directly at your host, you need to be sure of
either of two things:
Either of the above will allow you to receive mail directly at your host.
Try this:
# hostname
example.FreeBSD.org
# host example.FreeBSD.org
example.FreeBSD.org has address 204.216.27.XX
If that is what you see, mail directly to <[email protected]> should work without problems
(assuming sendmail is running correctly on example.FreeBSD.org).
If instead you see something like this:
# host example.FreeBSD.org
example.FreeBSD.org has address 204.216.27.XX
example.FreeBSD.org mail is handled (pri=10) by hub.FreeBSD.org
All mail sent to your host (example.FreeBSD.org) will end up
being collected on hub under the same username instead of being
sent directly to your host.
The above information is handled by your DNS server. The DNS record that carries mail
routing information is the Mail
eXchange entry. If no MX record
exists, mail will be delivered directly to the host by way of its IP address.
The MX entry for freefall.FreeBSD.org at one time looked like
this:
freefall MX 30 mail.crl.net
freefall MX 40 agora.rdrop.com
freefall MX 10 freefall.FreeBSD.org
freefall MX 20 who.cdrom.com
As you can see, freefall had many MX entries. The lowest MX
number is the host that receives mail directly if available; if it is not accessible for
some reason, the others (sometimes called “backup MXes”) accept messages
temporarily, and pass it along when a lower-numbered host becomes available, eventually
to the lowest-numbered host.
Alternate MX sites should have separate Internet connections from your own in order to
be most useful. Your ISP or another friendly site should have no problem providing this
service for you.
In order to set up a “mailhost” (a.k.a. mail server) you need to have any
mail sent to various workstations directed to it. Basically, you want to
“claim” any mail for any hostname in your domain (in this case *.FreeBSD.org) and divert it to your mail server so your users can
receive their mail on the master mail server.
To make life easiest, a user account with the same username should exist on both machines. Use adduser(8) to do
this.
The mailhost you will be using must be the designated mail exchanger for each
workstation on the network. This is done in your DNS configuration like so:
example.FreeBSD.org A 204.216.27.XX ; Workstation
MX 10 hub.FreeBSD.org ; Mailhost
This will redirect mail for the workstation to the mailhost no matter where the A
record points. The mail is sent to the MX host.
You cannot do this yourself unless you are running a DNS server. If you are not, or
cannot run your own DNS server, talk to your ISP or whoever provides your DNS.
If you are doing virtual email hosting, the following information will come in handy.
For this example, we will assume you have a customer with his own domain, in this case
customer1.org, and you want all the mail for customer1.org sent to your mailhost, mail.myhost.com. The entry in your DNS should look like this:
customer1.org MX 10 mail.myhost.com
You do not need an A record for
customer1.org if you only want to handle email for that
domain.
Note: Be aware that pinging customer1.org will not work
unless an A record exists for it.
The last thing that you must do is tell sendmail on your
mailhost what domains and/or hostnames it should be accepting mail for. There are a few
different ways this can be done. Either of the following will work:
-
Add the hosts to your /etc/mail/local-host-names file if you
are using the FEATURE(use_cw_file). If you are using a version
of sendmail earlier than 8.10, the file is /etc/sendmail.cw.
-
Add a Cwyour.host.com line to your /etc/sendmail.cf or /etc/mail/sendmail.cf
if you are using sendmail 8.10 or higher.
