When configuring a Postfix mail server, one common issue administrators encounter is the Recipient address rejected: User unknown in local recipient table error when sending emails to addresses within the same domain. This occurs specifically when attempting to send to addresses under your server's primary domain (e.g., test@example.com when your server is mail.example.com).

The error stems from Postfix's configuration in main.cf where the mydestination parameter isn't properly handling local domain delivery. In the provided configuration:

mydestination = $mydomain, localhost.$mydomain, localhost

The issue arises because Postfix considers itself the final destination for these domains but lacks proper user mapping.

Here are three approaches to resolve this:

Solution 1: Virtual Mailbox Domains

For modern Postfix setups using virtual mailboxes:

virtual_mailbox_domains = example.com
virtual_mailbox_maps = hash:/etc/postfix/virtual_mailbox
virtual_minimum_uid = 100
virtual_uid_maps = static:5000
virtual_gid_maps = static:5000

Create the virtual mailbox map file:

# /etc/postfix/virtual_mailbox
test@example.com   example.com/test/

Solution 2: Local Mailbox Configuration

For traditional local delivery:

mydestination = $myhostname, localhost.$mydomain, localhost
local_recipient_maps = $alias_maps unix:passwd.byname

Then ensure the user exists in the system:

sudo adduser test

Solution 3: Hybrid Approach

Combine both methods for flexibility:

mydestination = $myhostname, localhost.$mydomain, localhost
virtual_alias_maps = hash:/etc/postfix/virtual

Virtual aliases file example:

# /etc/postfix/virtual
test@example.com   realuser@otherdomain.com

After making changes, always:

sudo postfix check
sudo postfix reload

Test email delivery with:

echo "Test email" | mail -s "Test" test@example.com

Check logs with:

tail -f /var/log/mail.log

If issues persist, examine these Postfix parameters:

postconf -n

Key parameters to verify:

• mydomain should match your domain
• myorigin should be properly set
• inet_interfaces should include all necessary interfaces
• mynetworks should properly define trusted networks

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When configuring a Postfix mail server, one common issue arises when sending emails to addresses within the same domain as the server (e.g., mail.example.com trying to send to test@example.com). The server logs show:

Recipient address rejected: User unknown in local recipient table

This occurs because Postfix is configured to treat the domain as a local delivery domain but lacks proper user mapping.

The critical line in your main.cf is:

mydestination = $mydomain, localhost.$mydomain, localhost

This tells Postfix to handle mail for these domains locally, but without corresponding user accounts or virtual mailbox mappings, delivery fails.

Option 1: Virtual Mailbox Mapping

For production systems with multiple users, implement virtual mailbox mapping:

# Add to main.cf
virtual_mailbox_domains = example.com
virtual_mailbox_maps = hash:/etc/postfix/virtual_mailbox
virtual_minimum_uid = 1000
virtual_uid_maps = static:5000
virtual_gid_maps = static:5000

Then create /etc/postfix/virtual_mailbox:

test@example.com   example.com/test/

Option 2: Local Unix Accounts

For simple setups with few users:

# Create system account
sudo adduser testuser
# Set password
sudo passwd testuser
# Add to Postfix local_recipient_maps
local_recipient_maps = proxy:unix:passwd.byname $alias_maps

After changes, always test:

# Reload Postfix
sudo systemctl reload postfix
# Check configuration
postconf -n
# Test delivery
echo "Test email" | mail -s "Test" test@example.com

Enable verbose logging temporarily:

# In main.cf
debug_peer_list = example.com
debug_peer_level = 2

Then monitor logs:

tail -f /var/log/mail.log