When setting up a Postfix mail server with virtual mailboxes, you might encounter two particularly frustrating errors:

451 4.3.0 : Temporary lookup failure
550 5.1.1 : Recipient address rejected: User unknown in local recipient table

The "Temporary lookup failure" typically appears when Postfix can't access required database files. From the journalctl logs:

warning: hash:/etc/aliases is unavailable. open database /etc/aliases.db: No such file or directory
warning: hash:/etc/aliases lookup error for "dzervas@dzervas.gr"

This reveals Postfix is failing to access the aliases database. Even when you're using virtual mailboxes, Postfix still checks the system aliases by default.

The initial solution is straightforward:

# Create an empty aliases file if it doesn't exist
sudo touch /etc/aliases

# Generate the aliases.db file
sudo newaliases

After fixing the aliases issue, you'll likely encounter:

550 5.1.1 : Recipient address rejected: User unknown in local recipient table

This occurs because Postfix is still checking the local recipient table. The solution is to modify your main.cf:

# Disable local recipient checking when using virtual mailboxes
local_recipient_maps =

Even after these fixes, emails might queue but not deliver to the correct virtual mailbox location. Several configuration elements must work together:

# Main virtual mailbox settings
virtual_mailbox_base = /var/mail/vhost
virtual_mailbox_maps = hash:/etc/postfix/vmailbox
virtual_minimum_uid = 1000
virtual_uid_maps = static:2000
virtual_gid_maps = static:2000

# Make sure these are properly set
mydestination = localhost, localhost.$mydomain, $myhostname

Ensure your vmailbox file is properly formatted and compiled:

# Example vmailbox contents
dzervas@dzervas.gr      dzervas.gr/dzervas
dna@dzervas.gr          dzervas.gr/dna

# Compile the map
sudo postmap /etc/postfix/vmailbox

Proper permissions are crucial for virtual mailbox delivery:

# Create the base directory
sudo mkdir -p /var/mail/vhost
sudo chown -R 2000:2000 /var/mail/vhost
sudo chmod -R 700 /var/mail/vhost

After making changes, always test:

# Check Postfix configuration
sudo postfix check

# Reload Postfix
sudo systemctl reload postfix

# Verify virtual mailbox mapping
postmap -q "dzervas@dzervas.gr" hash:/etc/postfix/vmailbox

Ensure all these elements are in place:

• Properly compiled aliases database
• Correct virtual mailbox maps and permissions
• local_recipient_maps disabled when using virtual mailboxes
• mydestination not including virtual domains
• Proper filesystem permissions for the virtual mail directory

With these configurations in place, your Postfix virtual mail server should now properly receive and deliver emails to the designated virtual mailboxes.

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When configuring Postfix with virtual mailboxes, two critical errors commonly appear:

• "Temporary lookup failure" during SMTP transactions
• Mail getting queued but not delivered to virtual mailboxes

The key error in journalctl reveals:

error: open database /etc/aliases.db: No such file or directory
warning: hash:/etc/aliases is unavailable
warning: hash:/etc/aliases lookup error

This indicates Postfix is failing to access the aliases database, which is required even when using virtual mailboxes.

First, create a basic aliases file and compile it:

sudo touch /etc/aliases
sudo newaliases

Then modify main.cf to properly handle virtual delivery:

# Disable local recipient checking for virtual domains
local_recipient_maps =

# Ensure proper virtual mailbox delivery
virtual_mailbox_domains = dzervas.gr, ns0.dzervas.gr
virtual_transport = virtual
virtual_mailbox_limit = 51200000

Your vmailbox file format is correct, but ensure proper permissions:

sudo postmap /etc/postfix/vmailbox
sudo chown -R 2000:2000 /var/mail/vhost
sudo chmod -R 700 /var/mail/vhost

After making these changes, test with:

echo "Test email" | mail -s "Test" dzervas@dzervas.gr
postqueue -p

If mail gets stuck in queue, check master.cf for virtual transport:

virtual   unix  -       n       n       -       -       virtual

While DNS isn't strictly required for local testing, production requires:

dzervas.gr.      IN MX 10 ns0.dzervas.gr.
ns0.dzervas.gr.  IN A  192.0.2.1

Confirm virtual mailbox delivery works:

sudo ls -l /var/mail/vhost/dzervas.gr/dzervas
sudo postconf virtual_mailbox_domains

The key is ensuring all components - aliases, virtual maps, and transport - are properly configured and compiled.