Mail Server Management¶

Prerequisites¶

• Postfix installed
• MX record configured in DNS
• Firewall ports 25, 587 open

Procedure: Configure Postfix for a Domain¶

When to use: Setting up a mail server to handle email for a specific domain.

Steps:

1. Open /etc/postfix/main.cf.

2. Set key parameters:

   myhostname = mail.example.com
   mydomain = example.com
   myorigin = $mydomain
   inet_interfaces = all
   inet_protocols = all
   mydestination = $myhostname, localhost.$mydomain, localhost, $mydomain
   mynetworks = 127.0.0.0/8
   home_mailbox = Maildir/
   

3. Restart Postfix:

   systemctl restart postfix
   

Troubleshooting:

• "Address already in use": Check if another MTA (like Exim or Sendmail) is running.

Procedure: Send a Test Email¶

When to use: Verifying that Postfix can deliver mail locally or remotely.

Steps:

1. Send a test message:

   echo "Test body" | sendmail "centos@localhost"
   

2. Check logs for delivery status:

   tail -f /var/log/maillog
   

   Look for status=sent.

3. Check if the email has arrived in /home/centos/Maildir.

Troubleshooting:

• "Connection timed out": Firewall blocking port 25.
• "Relay access denied": You are trying to send mail through a server that doesn't trust your IP.

Procedure: Configure Dovecot IMAP¶

When to use: Allowing users to retrieve email using an email client (Outlook, Thunderbird).

Steps:

1. Edit /etc/dovecot/dovecot.conf:

   protocols = imap lmtp
   listen = *
   

2. Edit /etc/dovecot/conf.d/10-mail.conf:

   mail_location = maildir:~/Maildir
   

3. Edit /etc/dovecot/conf.d/10-auth.conf:

   disable_plaintext_auth = no
   auth_mechanisms = plain login
   

4. Restart Dovecot:

   systemctl restart dovecot
   

Troubleshooting:

• "Permission denied": Check permissions on user home directories and ~/Maildir.

Procedure: Set Up LMTP Between Postfix and Dovecot¶

When to use: Handing off local mail delivery from Postfix to Dovecot (better performance/indexing).

Steps:

1. Configure Dovecot socket /etc/dovecot/conf.d/10-master.conf:

   service lmtp {
     unix_listener /var/spool/postfix/private/dovecot-lmtp {
       mode = 0600
       user = postfix
       group = postfix
     }
   }
   

2. Configure Postfix to use LMTP /etc/postfix/main.cf:

   virtual_transport = lmtp:unix:private/dovecot-lmtp
   mailbox_transport = lmtp:unix:private/dovecot-lmtp
   

3. Restart both services.

Troubleshooting:

• "connect to private/dovecot-lmtp: No such file": Dovecot didn't create the socket or Postfix cannot access it (permissions).

Procedure: Test SMTP Submission with telnet¶

When to use: Verifying SMTP authentication and mail submission without using a mail client.

Steps:

1. Prepare base64-encoded credentials (copy command output use it later):

   printf '\0<username>\0<password>' | base64
   

2. Connect to port 587:

   # From remote machine (your personal computer)
   telnet mail.<your_vm_name>.sysadm.ee 587
   
   # OR from your VM
   telnet localhost 587
   

3. Identify to the server:

   EHLO <your_vm_name>.sysadm.ee
   

4. Authenticate:

   AUTH PLAIN <base64_string>
   

5. Send an email:

   MAIL FROM:<marketing@<your_vm_name>.sysadm.ee>
   RCPT TO:<nagios@scoring.sysadm.ee>
   DATA
   Subject: Test email
   
   This is a test message.
   .
   

6. Quit:

   QUIT
   

Troubleshooting:

• "Login failed": Check /var/log/maillog. Verify username, password and base64 string.

Procedure: Define an SPF record¶

When to use: To improve email deliverability and prevent spoofing, define an SPF record for your domain.

Steps:

1. Open you DNS Forward Zone file in /var/lib/knot/zones

2. Add a TXT record

<your_vm_name>.sysadm.ee. IN TXT "v=spf1 mx -all"

1. Validate the configuration:

   knotc conf-check
   knotc zone-check <zone>
   

2. Reload knotc:

   knotc reload
   

3. Verify:

   dig TXT <your_vm_name>.sysadm.ee
   

4. Note: The DNS changes might take time to propagate

Procedure: Test IMAP Login with telnet¶

When to use: Verifying IMAP authentication and connectivity without a heavy email client.

Steps:

1. Connect to port 143:

   telnet localhost 143
   

2. Login:

   a login <username> <password>
   

3. List folders:

   b list "" "*"
   

4. Logout:

   c logout
   

Troubleshooting:

• "Login failed": Check /var/log/maillog. Verify disable_plaintext_auth if testing without TLS.

Quick Reference¶

Related Documentation¶

• Technologies: Postfix, Dovecot
• Concepts: Email