SMTP 550 — Recipient Address Rejected (`erg.school`)

Date: 2026-04-30
Symptom: Access-link emails to @erg.school addresses fail with:

550 5.1.1 <user@erg.school>: Recipient address rejected: User unknown in virtual mailbox table

What is happening

The SMTP relay that XAMXAM uses to send outbound email is a Postfix instance that is also configured as the authoritative mail server for erg.school.

When XAMXAM sends RCPT TO:<user@erg.school>, Postfix looks up the address in its local virtual_mailbox_maps table. Because the individual mailbox does not exist in that table, Postfix rejects the message permanently with 550 instead of forwarding it outward.

This affects all outbound email to @erg.school sent through this relay, regardless of whether the address is real — Postfix never tries to route the message anywhere else.

Why it happens

Postfix owns a domain in one of two ways:

Setting	Effect
`mydestination`	Postfix delivers locally via Unix accounts
`virtual_mailbox_domains`	Postfix delivers locally via `virtual_mailbox_maps`

If erg.school (or a wildcard matching it) appears in either of these on the outbound relay, Postfix will never relay mail to that domain — it will always attempt local delivery and reject unknown recipients.

To confirm, run on the relay server:

postconf mydestination
postconf virtual_mailbox_domains
postconf relay_domains

Check whether erg.school appears (directly or via a lookup table).

Fix options

Option A — Preferred: use a different relay for outbound mail

Configure XAMXAM to send via an SMTP relay that does not host erg.school (e.g. a dedicated outbound relay, a transactional mail provider, or the outbound smarthost if one exists).

Change the SMTP settings in the XAMXAM admin panel (/admin/parametres.php) to point to that relay.

Option B — Remove `erg.school` from local delivery on the relay

If the relay should not be the final destination for erg.school mail, remove it from the relevant Postfix maps.

If it is in mydestination:

# /etc/postfix/main.cf
mydestination = localhost, localhost.localdomain
# remove erg.school (and any wildcard covering it)

If it is in virtual_mailbox_domains:

# /etc/postfix/main.cf
virtual_mailbox_domains = ...
# remove erg.school from the list (or from the referenced lookup table)

After editing main.cf:

postfix check
systemctl reload postfix

Option C — Add a `transport_maps` override for the domain

If erg.school must remain in virtual_mailbox_domains for inbound delivery but outbound mail from XAMXAM should still be relayed, add a transport override so that mail to erg.school sent by XAMXAM is forwarded to the real MX rather than delivered locally.

# /etc/postfix/main.cf
transport_maps = hash:/etc/postfix/transport

# /etc/postfix/transport
erg.school    smtp:[mail.erg.school]:25

postmap /etc/postfix/transport
systemctl reload postfix

Note: This approach is fragile — if XAMXAM is on the same server as the MX, you risk a delivery loop. Option A or B is cleaner.

Verification

After applying the fix, test with XAMXAM's built-in SMTP probe (/admin/parametres.php → Test SMTP). Then submit a real access request with an @erg.school address and confirm the email arrives.

You can also test directly from the server:

swaks --to test.user@erg.school \
      --from xamxam@erg.be \
      --server <smtp_host> --port 587 \
      --tls --auth-user <username> --auth-password <password>

A successful relay returns 250 2.0.0 Ok: queued as ….
A 550 response confirms the domain is still being caught locally.

3.7 KiB Raw Blame History

SMTP 550 — Recipient Address Rejected (erg.school)