Alias and Virtual Domains Configuration in Postfix: Complete Guide

Introduction

Managing email aliases and virtual domains in Postfix allows you to create flexible, scalable email infrastructures. Whether you need to forward emails from multiple addresses to a single mailbox, host email for multiple domains on one server, or create catch-all addresses, Postfix's alias and virtual domain capabilities provide powerful solutions.

Email aliases redirect messages from one address to another without creating separate mailboxes. For example, you can have [email protected], [email protected], and [email protected] all deliver to a single [email protected] mailbox. This simplifies management while presenting a professional, organized email structure to the outside world.

Virtual domains take this further by allowing a single mail server to handle email for multiple independent domains. You might host email for example.com, example.net, and client-domain.com all on one server, with each domain maintaining completely separate user accounts and aliases. This is essential for hosting providers, agencies managing client email, or organizations with multiple brands.

This comprehensive guide covers everything from simple aliases to complex virtual domain setups, including virtual mailboxes, virtual aliases, catch-all addresses, address extensions, and advanced routing configurations.

Prerequisites

Before configuring aliases and virtual domains, ensure you have:

System Requirements

• Working Postfix mail server
• Ubuntu 20.04/22.04, Debian 10/11, CentOS 8/Rocky Linux 8, or similar
• Root or sudo access
• Basic Postfix configuration completed

Mail Server Requirements

• Postfix installed and sending/receiving mail
• Dovecot configured (for virtual mailboxes)
• DNS records properly configured for all domains
• Understanding of current mail setup

Knowledge Prerequisites

• Linux command-line proficiency
• Basic Postfix configuration knowledge
• Understanding of email routing
• Text editor skills (nano, vim)

Understanding Aliases vs Virtual Domains

Local Aliases

Purpose: Redirect mail within the same domain Scope: System users and local delivery Configuration: /etc/aliases Use case: Small, single-domain setups

Example:

admin: root
support: admin
sales: admin, sales-team

Virtual Aliases

Purpose: Redirect mail for virtual domains Scope: Multiple domains, virtual users Configuration: /etc/postfix/virtual Use case: Multi-domain hosting

Example:

[email protected]       [email protected]
[email protected]     [email protected]
[email protected]       [email protected]

Virtual Mailboxes

Purpose: Actual mailbox storage for virtual domains Scope: Independent mailboxes for each address Configuration: /etc/postfix/vmailbox Use case: Complete virtual hosting solution

Example:

[email protected]        example.com/user/
[email protected]       example.net/admin/

Step 1: Configure Local Aliases

Local aliases are the simplest form of email forwarding.

Edit Aliases File

sudo nano /etc/aliases

Basic Alias Syntax

# Format: alias: destination
# One destination
postmaster: root

# Multiple destinations
admin: user1, user2, user3

# Forward to external email
webmaster: [email protected]

# Chain aliases
support: admin
admin: root
root: [email protected]

# Pipe to program
devnull: /dev/null
backups: |"/usr/local/bin/backup-handler.sh"

# Include file
team: :include:/etc/postfix/team-members.txt

Common Default Aliases

Add these standard aliases:

# Required aliases
postmaster: root
hostmaster: root
webmaster: root
abuse: root

# Administrative aliases
root: [email protected]
mailer-daemon: postmaster

# Department aliases
sales: [email protected]
support: [email protected]
info: [email protected]

Apply Alias Changes

After editing /etc/aliases:

# Rebuild alias database
sudo newaliases

# Or
sudo postalias /etc/aliases

# Reload Postfix
sudo systemctl reload postfix

Test Local Aliases

# Send test email
echo "Testing alias" | mail -s "Alias Test" postmaster

# Check delivery
sudo tail -f /var/log/mail.log

View Current Aliases

# List all aliases
cat /etc/aliases | grep -v "^#" | grep -v "^$"

# Search for specific alias
grep "postmaster" /etc/aliases

# Test alias resolution
postmap -q postmaster /etc/aliases

Step 2: Configure Virtual Alias Domains

Virtual alias domains forward all mail to other addresses.

Edit Postfix Main Configuration

sudo nano /etc/postfix/main.cf

Add or modify:

# Virtual alias domains
virtual_alias_domains = example.net example.org
virtual_alias_maps = hash:/etc/postfix/virtual

Create Virtual Alias File

sudo nano /etc/postfix/virtual

Add aliases:

# Format: virtual-address  real-address

# Simple forwarding
[email protected]               [email protected]
[email protected]             [email protected]

# Multiple destinations
[email protected]               [email protected], [email protected]

# Forward entire domain
@example.org                    [email protected]

# User-specific aliases
[email protected]                [email protected]
[email protected]                [email protected]

# Department aliases
[email protected]                [email protected]
[email protected]                [email protected]

# External forwarding
[email protected]           [email protected]

Compile and Apply

# Compile virtual alias database
sudo postmap /etc/postfix/virtual

# Reload Postfix
sudo systemctl reload postfix

Test Virtual Aliases

# Send test email
echo "Testing virtual alias" | mail -s "Test" [email protected]

# Check logs
sudo grep "example.net" /var/log/mail.log

# Test alias lookup
postmap -q [email protected] /etc/postfix/virtual

Step 3: Configure Virtual Mailbox Domains

Virtual mailbox domains provide independent mailboxes for each address.

Create Mail Storage User

# Create virtual mail user
sudo groupadd -g 5000 vmail
sudo useradd -g vmail -u 5000 vmail -d /var/mail/vmail -m -s /usr/sbin/nologin

# Create mail directory
sudo mkdir -p /var/mail/vmail
sudo chown -R vmail:vmail /var/mail/vmail
sudo chmod -R 770 /var/mail/vmail

Configure Postfix Main Settings

sudo nano /etc/postfix/main.cf

Add virtual mailbox configuration:

# Virtual mailbox settings
virtual_mailbox_domains = example.com example.net
virtual_mailbox_base = /var/mail/vmail
virtual_mailbox_maps = hash:/etc/postfix/vmailbox
virtual_uid_maps = static:5000
virtual_gid_maps = static:5000
virtual_alias_maps = hash:/etc/postfix/virtual

# Delivery method
virtual_transport = lmtp:unix:private/dovecot-lmtp

# Mailbox size limits
virtual_mailbox_limit = 0
message_size_limit = 52428800

Create Virtual Mailbox File

sudo nano /etc/postfix/vmailbox

Add mailboxes:

# Format: email-address  mailbox-path

# Domain: example.com
[email protected]               example.com/admin/
[email protected]               example.com/user1/
[email protected]               example.com/user2/
[email protected]               example.com/sales/

# Domain: example.net
[email protected]               example.net/admin/
[email protected]             example.net/contact/
[email protected]                example.net/info/

Mailbox paths are relative to virtual_mailbox_base. Full path: /var/mail/vmail/example.com/admin/

Create Virtual Domains File

sudo nano /etc/postfix/vdomains

List virtual domains:

example.com     OK
example.net     OK
example.org     OK

Update main.cf:

sudo nano /etc/postfix/main.cf

Change:

virtual_mailbox_domains = hash:/etc/postfix/vdomains

Compile Databases

# Compile mailbox database
sudo postmap /etc/postfix/vmailbox

# Compile domains database
sudo postmap /etc/postfix/vdomains

# Compile virtual aliases
sudo postmap /etc/postfix/virtual

# Reload Postfix
sudo systemctl reload postfix

Integrate with Dovecot

Dovecot must be configured for virtual users:

sudo nano /etc/dovecot/conf.d/10-mail.conf

Set:

mail_location = maildir:/var/mail/vmail/%d/%n/Maildir
mail_uid = vmail
mail_gid = vmail
first_valid_uid = 5000
last_valid_uid = 5000

Variables:

• %d = domain (example.com)
• %n = username (admin)
• Full path: /var/mail/vmail/example.com/admin/Maildir

Create Virtual Users

For authentication, create users in Dovecot:

sudo nano /etc/dovecot/users

Add users with encrypted passwords:

[email protected]:{SHA512-CRYPT}$6$rounds=100000$...
[email protected]:{SHA512-CRYPT}$6$rounds=100000$...
[email protected]:{SHA512-CRYPT}$6$rounds=100000$...

Generate passwords:

# Generate encrypted password
doveadm pw -s SHA512-CRYPT -p 'SecurePassword123'

# Add user
echo "[email protected]:$(doveadm pw -s SHA512-CRYPT -p 'Password')" | sudo tee -a /etc/dovecot/users

# Set permissions
sudo chmod 640 /etc/dovecot/users
sudo chown root:dovecot /etc/dovecot/users

Step 4: Configure Catch-All Addresses

Catch-all addresses receive mail sent to any non-existent address in a domain.

Virtual Domain Catch-All

sudo nano /etc/postfix/virtual

Add:

# Catch-all for example.com
@example.com                    [email protected]

# Catch-all for example.net
@example.net                    [email protected]

# Catch-all forwarding to external
@example.org                    [email protected]

Specific User Catch-All

# Catch all mail for user
user+*@example.com              [email protected]

# Catch all subaddresses
admin+*@example.com             [email protected]

Compile and Apply

sudo postmap /etc/postfix/virtual
sudo systemctl reload postfix

Test Catch-All

# Send to non-existent address
echo "Test catch-all" | mail -s "Test" [email protected]

# Check delivery
sudo tail -f /var/log/mail.log

Disable Catch-All

To disable catch-all for a domain:

sudo nano /etc/postfix/virtual

Remove the @example.com line, or comment it:

# @example.com                  [email protected]

Compile and reload:

sudo postmap /etc/postfix/virtual
sudo systemctl reload postfix

Step 5: Configure Address Extensions

Address extensions (also called plus addressing or subaddressing) allow users to create unlimited variations of their email address.

Format: [email protected]

Enable in Postfix

sudo nano /etc/postfix/main.cf

Add:

# Enable address extensions
recipient_delimiter = +

Configure in Dovecot

sudo nano /etc/dovecot/conf.d/15-lda.conf

Add:

protocol lda {
  # Enable address extensions
  recipient_delimiter = +

  # Deliver extensions to main mailbox
  lda_mailbox_autocreate = yes
  lda_mailbox_autosubscribe = yes
}

Reload Services

sudo systemctl reload postfix
sudo systemctl reload dovecot

Use Cases

Email organization:

[email protected]    # Newsletter signups
[email protected]      # Online shopping
[email protected]        # Social media
[email protected]          # Work-related

Spam tracking:

[email protected]      # Track which companies leak addresses
[email protected]

Filtering: Create filters in email client to automatically sort messages:

If To contains "user+newsletter"
  Move to "Newsletters" folder

Test Address Extensions

# Send to extended address
echo "Testing extension" | mail -s "Test" [email protected]

# Verify delivery to main mailbox
# Check [email protected] inbox

Step 6: Advanced Virtual Domain Configuration

Multiple Virtual Alias Maps

For better organization, split aliases across multiple files:

sudo nano /etc/postfix/main.cf

Configure:

virtual_alias_maps =
    hash:/etc/postfix/virtual,
    hash:/etc/postfix/virtual-aliases-example-com,
    hash:/etc/postfix/virtual-aliases-example-net

Create separate files:

# Example.com aliases
sudo nano /etc/postfix/virtual-aliases-example-com

# Example.net aliases
sudo nano /etc/postfix/virtual-aliases-example-net

Compile all:

sudo postmap /etc/postfix/virtual-aliases-example-com
sudo postmap /etc/postfix/virtual-aliases-example-net
sudo systemctl reload postfix

Regex-Based Aliases

For complex matching patterns:

sudo nano /etc/postfix/main.cf

Add:

virtual_alias_maps =
    hash:/etc/postfix/virtual,
    regexp:/etc/postfix/virtual-regexp

Create regex file:

sudo nano /etc/postfix/virtual-regexp

Add patterns:

# Format: /pattern/ destination

# Catch all admin variants
/^admin[0-9]*@example\.com$/    [email protected]

# Catch all support variants
/^(support|help|assist)@example\.com$/  [email protected]

# Redirect old domain
/^(.+)@old-domain\.com$/        ${1}@new-domain.com

# Convert dots to plus
/^([^+]+)\.([^@]+)@example\.com$/  ${1}+${2}@example.com

No compilation needed for regexp maps. Reload:

sudo systemctl reload postfix

Per-Domain Catch-All with Exceptions

sudo nano /etc/postfix/virtual

Configure:

# Specific addresses (processed first)
[email protected]               [email protected]
[email protected]             [email protected]

# Catch-all (processed after specific matches)
@example.com                    [email protected]

Postfix processes entries in order, so specific matches take precedence.

Step 7: Managing Virtual Domains

Add New Domain

# 1. Add to virtual domains
echo "newdomain.com    OK" | sudo tee -a /etc/postfix/vdomains
sudo postmap /etc/postfix/vdomains

# 2. Add mailboxes
sudo nano /etc/postfix/vmailbox

Add:

[email protected]             newdomain.com/admin/
[email protected]           newdomain.com/contact/

Compile:

sudo postmap /etc/postfix/vmailbox

Add users:

# 3. Add Dovecot users
echo "[email protected]:$(doveadm pw -s SHA512-CRYPT -p 'Password')" | sudo tee -a /etc/dovecot/users

Create directory:

# 4. Create mail directory
sudo mkdir -p /var/mail/vmail/newdomain.com
sudo chown -R vmail:vmail /var/mail/vmail/newdomain.com

Configure DNS:

# 5. Add DNS records
# MX record: newdomain.com -> mail.example.com
# A record: mail.newdomain.com -> your-ip
# SPF record: v=spf1 mx a ip4:your-ip ~all

Reload:

sudo systemctl reload postfix dovecot

Remove Domain

# 1. Remove from virtual domains
sudo nano /etc/postfix/vdomains
# Remove or comment out the domain

sudo postmap /etc/postfix/vdomains

# 2. Remove mailboxes
sudo nano /etc/postfix/vmailbox
# Remove domain mailboxes

sudo postmap /etc/postfix/vmailbox

# 3. Remove users
sudo nano /etc/dovecot/users
# Remove domain users

# 4. Backup and remove mail
sudo tar czf domain-backup.tar.gz /var/mail/vmail/olddomain.com/
sudo rm -rf /var/mail/vmail/olddomain.com/

# 5. Reload
sudo systemctl reload postfix dovecot

List All Domains

# List virtual mailbox domains
postconf virtual_mailbox_domains

# List from file
cat /etc/postfix/vdomains | grep -v "^#"

# Count domains
cat /etc/postfix/vdomains | grep -v "^#" | wc -l

List All Mailboxes

# List all virtual mailboxes
cat /etc/postfix/vmailbox | grep -v "^#"

# List mailboxes for specific domain
grep "@example.com" /etc/postfix/vmailbox

# Count mailboxes
cat /etc/postfix/vmailbox | grep -v "^#" | wc -l

Step 8: Testing and Verification

Test Alias Resolution

# Test local alias
postmap -q postmaster /etc/aliases

# Test virtual alias
postmap -q [email protected] /etc/postfix/virtual

# Test virtual mailbox
postmap -q [email protected] /etc/postfix/vmailbox

# Test domain
postmap -q example.com /etc/postfix/vdomains

Test Mail Delivery

# Send to alias
echo "Test alias" | mail -s "Alias Test" [email protected]

# Send to virtual mailbox
echo "Test mailbox" | mail -s "Mailbox Test" [email protected]

# Send to catch-all
echo "Test catchall" | mail -s "Catchall Test" [email protected]

# Send with extension
echo "Test extension" | mail -s "Extension Test" [email protected]

Check Logs

# Monitor mail log
sudo tail -f /var/log/mail.log

# Check specific delivery
sudo grep "[email protected]" /var/log/mail.log | tail -20

# Check bounces
sudo grep "bounced" /var/log/mail.log | tail -20

Verify Mailbox Creation

# List mail directories
sudo ls -la /var/mail/vmail/

# Check specific mailbox
sudo ls -la /var/mail/vmail/example.com/admin/Maildir/

# Check mail files
sudo find /var/mail/vmail/ -name "cur" -type d -exec ls -la {} \;

Troubleshooting Common Issues

Issue 1: Alias Not Working

Symptoms: Email not forwarded to destination

Diagnosis:

# Test alias lookup
postmap -q [email protected] /etc/postfix/virtual

# Check logs
sudo grep "[email protected]" /var/log/mail.log

Solutions:

# Recompile database
sudo postmap /etc/postfix/virtual

# Check syntax
cat /etc/postfix/virtual | grep [email protected]

# Reload Postfix
sudo systemctl reload postfix

Issue 2: Virtual Domain Not Receiving Mail

Symptoms: Mail to virtual domain bounces

Diagnosis:

# Check if domain is listed
postconf virtual_mailbox_domains

# Check domain file
grep "example.com" /etc/postfix/vdomains

# Check MX record
dig example.com MX +short

Solutions:

# Add domain
echo "example.com    OK" | sudo tee -a /etc/postfix/vdomains
sudo postmap /etc/postfix/vdomains

# Verify main.cf
sudo postconf | grep virtual_mailbox_domains

# Reload
sudo systemctl reload postfix

Issue 3: Permission Denied

Symptoms: "permission denied" errors in logs

Diagnosis:

# Check ownership
sudo ls -la /var/mail/vmail/

# Check processes
ps aux | grep -E "postfix|dovecot"

Solutions:

# Fix ownership
sudo chown -R vmail:vmail /var/mail/vmail/

# Fix permissions
sudo chmod -R 770 /var/mail/vmail/

# Restart services
sudo systemctl restart postfix dovecot

Issue 4: Catch-All Not Working

Symptoms: Mail to non-existent addresses bounces instead of going to catch-all

Diagnosis:

# Check virtual aliases
grep "@example.com" /etc/postfix/virtual

# Test lookup
postmap -q [email protected] /etc/postfix/virtual

Solutions:

# Add catch-all
echo "@example.com    [email protected]" | sudo tee -a /etc/postfix/virtual

# Recompile
sudo postmap /etc/postfix/virtual

# Ensure no reject_unverified_recipient
sudo postconf | grep reject_unverified_recipient

# Reload
sudo systemctl reload postfix

Issue 5: Address Extensions Not Delivered

Symptoms: mail to [email protected] bounces

Diagnosis:

# Check recipient delimiter
postconf recipient_delimiter

# Check Dovecot config
doveconf -n | grep recipient_delimiter

Solutions:

# Set delimiter in Postfix
sudo postconf -e "recipient_delimiter = +"

# Set in Dovecot
sudo nano /etc/dovecot/conf.d/15-lda.conf

Add:

recipient_delimiter = +

Reload:

sudo systemctl reload postfix dovecot

Best Practices

1. Organization

• Use descriptive alias names
• Group related aliases
• Document purpose of complex aliases
• Keep separate files for different domains

2. Security

# Restrict file permissions
sudo chmod 640 /etc/postfix/virtual
sudo chmod 640 /etc/postfix/vmailbox
sudo chmod 640 /etc/dovecot/users

# Set proper ownership
sudo chown root:postfix /etc/postfix/virtual
sudo chown root:postfix /etc/postfix/vmailbox

3. Maintenance

• Regularly review and clean up unused aliases
• Remove bouncing destinations
• Update aliases when staff changes
• Backup alias files before changes

4. Documentation

Create an alias inventory:

sudo nano /etc/postfix/README-aliases.txt

Document:

Domain: example.com
Purpose: Main company domain

Aliases:
- [email protected] -> forwards to admin-team
- [email protected] -> forwards to CRM system
- [email protected] -> forwards to ticket system
- @example.com -> catch-all to admin (temporary)

Last updated: 2026-01-11
Contact: [email protected]

5. Testing

After any changes:

# 1. Check syntax
sudo postfix check

# 2. Test lookups
postmap -q [email protected] /etc/postfix/virtual

# 3. Send test email
echo "Test" | mail -s "Test" [email protected]

# 4. Verify in logs
sudo tail -f /var/log/mail.log

Conclusion

You now have comprehensive alias and virtual domain configuration for Postfix, enabling you to manage complex email routing, host multiple domains, and create flexible addressing schemes. This setup provides the foundation for professional, scalable email infrastructure.

Key Accomplishments

1. Local Aliases: Simple forwarding within primary domain
2. Virtual Aliases: Cross-domain and multi-domain forwarding
3. Virtual Mailboxes: Complete virtual domain hosting
4. Catch-All Addresses: Flexibility in receiving mail
5. Address Extensions: Enhanced organization and filtering

Next Steps

1. Add more domains: Expand virtual hosting as needed
2. Implement automation: Scripts for adding users/domains
3. Set up quotas: Limit mailbox sizes per user/domain
4. Configure webmail: Browser-based access (Roundcube/Rainloop)
5. Implement backup: Automated backup of mail and configurations

Important Reminders

• Compile after changes: Always run postmap after editing map files
• Reload services: Run systemctl reload postfix to apply changes
• Test thoroughly: Verify each alias and domain works correctly
• Document configuration: Keep records of aliases and their purposes
• Backup regularly: Protect alias configurations and mailbox data

With these alias and virtual domain configurations in place, you have a flexible, scalable email system capable of growing with your needs while maintaining organization and manageability.