• SendMailConfiguration

SendMail Configuration

Overview

Configuring sendmail MTA has a huge literature, only small tips will be described here.

The basis is the simple default configuration file on CentOS. See /etc/mail/sendmail.mc.orig. The goal of the changes to relay all outgoing emails from my CentOS workstations to my ISP and masquerade the domain and even the real linux user name to my email address at the ISP. See the complete configuration file /etc/mail/sendmail.mc.

Relay All Outgoing Mail to the ISP with Authentication

The following changes were performed in /etc/mail/sendmail.mc:

[root@centos1 mail]# diff sendmail.mc sendmail.mc.orig
26c26
< define(`SMART_HOST', `mail.hu.inter.net')dnl
---
> dnl define(`SMART_HOST', `smtp.your.provider')dnl
78d77
< FEATURE(`authinfo',`hash -o /etc/mail/authinfo.db')dnl

where mail.hu.inter.net is the SMTP server of my ISP. The /etc/mail/authinfo.db is created from the /etc/mail/authinfo file:

[root@centos1 mail]# cd /etc/mail
[root@centos1 mail]# vi authinfo
   # Add the following line (AuthInfo:ISP SMTP server "U:SMTP user" "P:SMTP password" "M:method"):
   AuthInfo:mail.hu.inter.net "U:nagyt@hu.inter.net" "P:Password to the SMTP server" "M:PLAIN"
[root@centos1 mail]# chmod 640 authinfo
[root@centos1 mail]# makemap hash /etc/mail/authinfo < /etc/mail/authinfo

Start service saslauthd as root to allow sendmail to use authentication.

chkconfig saslauthd on
chkconfig --list saslauthd
service saslauthd start

Masquerading User and Domain Name

Masquerading User and Domain Name is necessary to have real domain name, an email address in sender address. E.g: root@centos1.tibi1959.hu will be converted to nagyt@hu.inter.net. The following changes were performed in /etc/mail/sendmail.mc:

[root@centos1 mail]# diff sendmail.mc sendmail.mc.orig
< dnl # Use generics table for masquerading
< dnl #
< FEATURE(genericstable, hash /etc/mail/generics)dnl
< GENERICS_DOMAIN(centos1.tibi1959.hu)dnl
< dnl #
166c160
< MASQUERADE_AS(`hu.inter.net')dnl
---
> dnl MASQUERADE_AS(`mydomain.com')dnl
170c164
< FEATURE(masquerade_envelope)dnl
---
> dnl FEATURE(masquerade_envelope)dnl

where hu.inter.net is the domain name of my ISP, centos1.tibi1959.hu is my internal domain name. The /etc/mail/generics.db is created from the file /etc/mail/generics:

[root@centos1 mail]# cd /etc/mail
[root@centos1 mail]# vi generics
   # Add the following lines ("User name" "Full email address"), to allow root, ntibor and apache to send emails:
   root    nagyt@hu.inter.net
   ntibor  nagyt@hu.inter.net
   apache  nagyt@hu.inter.net
[root@centos1 mail]# chmod 640 generics
[root@centos1 mail]# makemap hash /etc/mail/generics < /etc/mail/generics

Restarting sendmail

After all configurations are done, recreate /etc/mail/sendmail.cf and restart sendmail:

[root@centos1 mail]# cd /etc/mail
[root@centos1 mail]# make all -C /etc/mail
[root@centos1 mail]# /etc/init.d/sendmail restart