Sendmail is a general purpose email routing facility used for email transport over the Internet. It includes SMTP (Simple Mail Transfer Protocol) for the mail-transfer and email delivery. Most of the system administrators preferred to use Sendmail server as MTA than other MTAs. You can also use Sendmail server to send the email via external SMTP servers like Gmail, Amazon SES, MailChimp etc.
1. Install Sendmail
If you don’t have installed Sendmail using the following command to install Sendmail with other required packages using yum package manager.
sudo dnf install sendmail sendmail-cf
2. Configure Sendmail on Fedora
Before starting configuration we must know about various Sendmail configuration files exists in /etc/mail directory.
- access — Allow/Deny other systems to use Sendmail for outbound emails.
- domaintable — Used for domain name mapping for Sendmail.
- local-host-names — Used to define aliases for the host.
- mailertable — Defined the instructions that override routing for particular domains.
- virtusertable — Specifies a domain-specific form of aliasing, allowing multiple virtual domains to be hosted on one machine.
2.1 Comment out below line in /etc/mail/sendmail.mc to allow receiving email from anywhere. To comment a line in sendmail.mc, just put dnl at start of line.
dnl DAEMON_OPTIONS(`Port=smtp,Addr=127.0.0.1, Name=MTA')dnl
2.2 Add this line also in sendmail.mc above ‘MAILER’ option
FEATURE(`relay_hosts_only')dnl
2.3 Add your PC’s full hostname in this file.
hostname >> /etc/mail/relay-domains
3. Recompile Configuration File
m4 ia a macro processor to compile the Sendmail configuration files. m4 is stream-based, that is, it doesn’t understand about lines.
sudo m4 /etc/mail/sendmail.mc > /etc/mail/sendmail.cf
Restart Sendmail service
sudo systemctl restart sendmail
4. Configure Domain-based E-mail Routing
As we read above that virtusertable file used for aliasing, allowing multiple virtual domains to be hosted on one machine.
- 1. All emails addressed to @example.com domain delivered to support@mydomain.com
@example.com support@mydomain.com
- 2. All emails addressed to support@mydomain.com will forward to local user jack.
support@mydomain.com jack
- 3. All emails addressed to @mydomain.com will forward to domain @otherdomain.com with corresponding usernames.
@mydomain.com %1@otherdomain.com
- 4. All emails addressed to @otherdomain.com will be rejected my mail server with acknowledging sender with the message
@otherdomain.com error:nouser User unknown
After making all changes in virtusertable execute following command to create updated virtusertable.db file containing the new configuration.
makemap hash /etc/mail/virtusertable < /etc/mail/virtusertable
Finally, restart the Sendmail service to apply changes
sudo systemctl restart sendmail
Thanks for reading this article. I hope this article will help you to configure Sendmail on Fedora systems.
References:
http://www.sendmail.com/
http://www.sendmail.com/sm/open_source/docs/m4/intro_m4.html
1 Comment
Thank you very much for this tutorial. In the past I’ve struggled to get sendmail working on new machines, and sometimes after an OS upgrade. This tutorial could have saved me a lot of wasted time. However there is a small item that could be added. My first attempt to use sendmail after following your instructions produced what seemed to be a ‘hung’ sendmail process, with this message:
‘sendmail.service: Can’t open PID file /run/sendmail.pid (yet?) after start: Operation not permitted’
After a little research I found the solution here: https://linuxconfig.org/sendmail-unqualified-hostname-unknown-sleeping-for-retry-unqualified-hostname
i.e.
sendmail is searching for a FQDN ( fully qualified domain name ). In our case the host name is “debian” and that is not a FQDN. To resolve this problem change /etc/hosts: FROM:
127.0.0.1 localhost
127.0.1.1 debian
TO:
127.0.0.1 localhost.localdomain localhost debian
127.0.1.1 debian
I suggest that your tutorial would be even more valuable to more people if you included that tip (replacing ‘debian’ with the hostname of the machine being used).
Thanks
Aaron Sloman