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Set up forwarding with Postfix by declaring your domain as a virtual_alias_domain, mapping each full recipient address in virtual_alias_maps, compiling that map with postmap, and reloading Postfix. Keep the domain out of mydestination and relay_domains, then verify DNS, delivery, and relay restrictions before accepting real mail.
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What Postfix email forwarding does
Postfix can accept mail for a domain hosted on your VPS and redirect each recipient to another mailbox, such as Gmail or an address at a different provider. The forwarding decision is made with a virtual alias map. For example, mail addressed to [email protected] can be delivered to joe@somewhere without creating a local Linux account named joe.
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Virtual aliasing changes the SMTP envelope recipient used for delivery. It does not rewrite the message headers, so the original To: and other headers remain in the message. Aliases are recursive: if one destination is itself another alias, Postfix follows the chain until it reaches a final destination. A circular chain can create a delivery loop.
This setup is an address-routing function, not a complete mail-hosting stack. Postfix accepts the message for the domain, looks up the recipient, and submits the resulting delivery. It does not create mailboxes, provide webmail, or guarantee that a destination provider will place the forwarded message in the inbox. Treat the alias table as a deliberate list of addresses you own and maintain.
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Prerequisites on the VPS and domain
- A Linux VPS with Postfix installed and administrative access through
sudo. - A stable public IP address and a domain whose DNS you control.
- An MX record that directs the domain to this VPS, or to the intended inbound mail host.
- Reverse DNS configured when required by your VPS provider or recipient systems.
- A clear understanding of the provider’s TCP port 25 policy and firewall rules.
Confirm which host is actually intended to receive inbound mail before editing Postfix. An MX record pointing at another service means that service, not this VPS, will receive the message. If the domain has multiple MX records, delivery can be attempted against more than one host, so each listed destination must be intentional.
Postfix configuration alone cannot guarantee that every recipient provider will accept forwarded mail. Some VPS networks restrict direct outbound SMTP, and recipient systems evaluate the sending IP, reverse DNS, authentication, reputation, and message policies independently. If direct delivery is unsuitable, configure an authenticated or otherwise approved SMTP relay (smarthost) instead of attempting to bypass the provider’s restrictions.
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Choose the right alias mechanism
| Mechanism | Address matched | Typical destination | Use it when |
|---|---|---|---|
/etc/aliases with alias_maps |
Local part on the server | Local users, commands, or local mailboxes | You are handling recipients considered local by Postfix |
virtual_alias_maps |
Full address, including domain | Remote addresses such as another provider’s mailbox | You are forwarding addresses in a hosted virtual domain |
For domain forwarding, use the second mechanism. A local alias file does not replace the virtual-domain declaration, and adding a full address to /etc/aliases will not correctly classify an Internet-facing hosted domain.
The distinction matters when you host more than one domain. Local aliases are evaluated in the context of recipients Postfix considers local; virtual aliases explicitly match an address such as [email protected]. Keeping those address classes separate makes later troubleshooting easier and prevents a local account name from accidentally becoming a public forwarding address.
Classify the forwarding domain correctly
Postfix must know that the domain is a virtual alias domain. Put it in virtual_alias_domains and do not also list it in mydestination or relay_domains. A domain in the wrong class can produce relay access denied
, or cause the server to report mail loops back to myself
.
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The domain entry is required even when every individual recipient has a mapping. It tells Postfix to accept the domain for virtual-alias processing rather than treating it as a local mailbox domain or a relay destination.
Think of the settings as separate questions. virtual_alias_domains answers which domains this alias service accepts. virtual_alias_maps answers what to do with each accepted address. relay_domains is an authorization list for relaying, not a substitute for the alias-domain list. Mixing these roles is a common cause of confusing SMTP responses.
Configure Postfix virtual aliases
1. Check the available map types
Postfix installations do not all provide the same database back ends. Display the types compiled into your installation:
postconf -mhash: is common on many systems. The Postfix documentation also uses lmdb:. Use a type shown by postconf -m; the prefix in virtual_alias_maps must match the type you use when building and querying the map.
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Do not assume that a command copied from another distribution will work unchanged. If lmdb is not listed, choose an available type such as hash. Conversely, if the configuration names lmdb:, building a hash database will not update the map Postfix reads.
2. Set the virtual-domain and map settings
Edit /etc/postfix/main.cf and add or adjust these parameters. This example uses the LMDB form documented by Postfix:
virtual_alias_domains = example.com
virtual_alias_maps = lmdb:/etc/postfix/virtualReplace example.com with your domain. If your system supports only a hash map, use:
virtual_alias_maps = hash:/etc/postfix/virtualDo not leave the forwarding domain in a conflicting mydestination or relay_domains entry. Preserve unrelated domains that the server genuinely handles; remove only the domain you are converting to virtual aliasing.
Inspect the effective configuration rather than relying only on the text you remember editing. postconf virtual_alias_domains virtual_alias_maps mydestination relay_domains displays the active values, including values supplied by distribution defaults or included configuration files.
3. Create recipient mappings
Create /etc/postfix/virtual with one mapping per line. The left side is the complete address that Postfix should accept; the right side is the final destination:
# /etc/postfix/virtual
[email protected] postmaster
[email protected] joe@somewhere
[email protected] jane@somewhere-elseThe first example sends mail to a local destination named postmaster. The other entries redirect to remote addresses. Use spaces or tabs between the address and destination, and place comments on lines beginning with #.
Use the exact domain spelling on the left side, and keep one authoritative entry for each address. A typo in the local part or domain is not a near match: it produces no exact lookup. If the destination is another alias, document that intentionally so an administrator can follow the chain without guessing.
Virtual aliases can be recursive. If you intentionally need recursion to stop at a particular address, alias that address to itself; otherwise, correct any chain that eventually points back to an earlier recipient. An accidental cycle can result in repeated attempts or a loop diagnostic.
4. Optionally add a catch-all carefully
A catch-all entry has the form:
@example.com [email protected]It redirects any address in the domain that is not matched by a more specific entry. Catch-alls can attract misaddressed mail, backscatter, and abuse, so add one only when you have a deliberate reason and have tested its effect. A normal forwarding setup should usually list the recipients it actually intends to serve.
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Test a catch-all with an address that has no explicit entry, not just with a known address. Otherwise, an unintended catch-all can remain hidden while accepting spam, automated probes, and mail for mistyped users. Removing the catch-all later also requires rebuilding the map and rechecking that an unmapped recipient is rejected.
5. Build the lookup database and reload
After every edit to the source file, rebuild the indexed map using the same path and map type configured in main.cf:
sudo postmap /etc/postfix/virtual
sudo postfix check
sudo postfix reloadpostmap creates or updates the database beside the source file. A hash map commonly produces /etc/postfix/virtual.db; LMDB creates its corresponding database files. postfix check validates the installation and permissions, while postfix reload makes the new configuration available to running processes.
Run postmap after every change, even if the edit appears minor. Postfix normally consults the indexed database, not the plain-text file at delivery time. A successful reload without a newly compiled map leaves the old recipient values in effect.
Set DNS and understand outbound delivery
Inbound MX routing
Publish an MX record that points the forwarding domain to the VPS or to the inbound host that actually runs Postfix. If the MX points elsewhere, messages will never reach this configuration, regardless of how correct the alias map is.
Allow time for DNS changes to propagate according to the record’s TTL, and query the public DNS view used by senders rather than checking only a local resolver. Also verify that the MX hostname resolves to the intended public address and that the VPS accepts SMTP on that address.
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| Consideration | Direct delivery from the VPS | Authenticated SMTP relay |
|---|---|---|
| Sending IP and reverse DNS | You control the VPS address and must maintain suitable reverse DNS. | The relay supplies its own sending infrastructure; your VPS need not deliver directly. |
| Port 25 policy | Requires outbound SMTP access from the provider and network. | Can use the relay’s approved submission or SMTP service when port 25 is restricted. |
| Authentication and encryption | Depends on the recipient-to-recipient SMTP connection. | Usually configured with the relay’s authentication and encryption requirements. |
| Queue and bounce handling | Postfix on your VPS queues messages and receives delivery responses. | The relay handles part of the onward queueing and feedback path. |
| Reputation management | Your VPS IP reputation affects acceptance. | The relay’s infrastructure and policies affect acceptance. |
| Operational cost | Fewer direct service fees, but you carry DNS, reputation, monitoring, and delivery work. | May add a provider charge or sending limits, in exchange for less direct delivery administration. |
| Operational dependence | Fewer third-party dependencies but more responsibility for DNS, reputation, and delivery. | Less direct delivery administration but dependence on the relay’s availability, limits, and terms. |
Postfix does not promise universal inbox placement. SPF, DKIM, DMARC, reverse DNS, and provider reputation are separate deployment concerns; a virtual alias only determines where Postfix forwards a message after accepting it. Forwarding can also make authentication alignment and spam evaluation more complicated at the destination, so inspect destination-provider feedback instead of treating acceptance by your VPS as proof of successful delivery.
Prevent the VPS from becoming an open relay
A forwarding server exposed to the Internet must accept mail for its own hosted domain without allowing arbitrary strangers to submit mail to arbitrary external destinations. In Postfix, mynetworks identifies authorized client networks, while relay_domains identifies destinations for which relaying is permitted. The basic configuration also permits forwarding from authorized networks by default, so those networks must be narrow.
- Keep
mynetworkslimited to localhost and explicitly authorized systems that really need to submit mail. - Do not authorize an Internet-facing subnet merely because it is convenient.
- Review
relay_domainsand recipient restrictions before exposing SMTP on a public address. - Do not use a catch-all unless you have tested its abuse and backscatter consequences.
- After changes, test both an intended recipient and an unrelated, unmapped recipient from an external account.
The goal is asymmetric behavior: mail addressed to your declared virtual domain is accepted and mapped, while an unauthenticated sender cannot use your host as a general-purpose relay.
Use a test account outside the trusted networks when checking this behavior. A submission from localhost or another address in mynetworks may be authorized by design and therefore cannot prove that anonymous Internet clients are blocked. Review the effective network list with postconf -n and remove broad ranges that are not required.
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Verify the configuration before relying on it
Check effective settings
sudo postfix check
postconf -nReview the output for the intended virtual_alias_domains, virtual_alias_maps, network permissions, and relay settings. The postconf -n output shows non-default settings, which makes conflicting entries easier to spot.
Confirm the map database and query a recipient
Make sure the generated database exists next to the source file. Then query the exact address with the configured map type:
postmap -q '[email protected]' hash:/etc/postfix/virtualSubstitute lmdb: if that is the type in virtual_alias_maps. The command should return the destination configured for that address. An empty result means there is no exact mapping in that database; check spelling, domain, whitespace, and whether you rebuilt the map after editing.
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Send controlled test messages
- Send a message to a mapped address from an unrelated external account.
- Confirm that the destination mailbox receives it and inspect the received headers to verify the original message context is intact.
- Check the sender’s mail log for queue, delivery, defer, or rejection details.
- Send to an unmapped address and verify that Postfix rejects it rather than accepting it as an unintended catch-all.
- If a catch-all is present, test an address that has no explicit entry and confirm the result is intentional.
Use your distribution’s mail-log location and standard log tools to inspect the transaction. A successful SMTP acceptance is not the same as final delivery; the onward destination can still defer or reject the message. Record the remote response when troubleshooting, because a DNS failure, connection refusal, temporary deferral, and policy rejection require different remedies.
Troubleshoot common failures
“Relay access denied” or “mail loops back to myself”
Check that the domain appears in virtual_alias_domains and is absent from conflicting mydestination and relay_domains entries. Rebuild /etc/postfix/virtual with the configured map type, run postfix check, and reload Postfix.
Edits have no effect
Postfix reads the indexed database, not the plain-text source file at delivery time. Run postmap against the exact file named in virtual_alias_maps, use the same hash: or lmdb: prefix, and reload the service. Query the rebuilt map with postmap -q to confirm the new value.
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This usually indicates that the request is being handled through /etc/aliases. For a domain address such as [email protected], define a virtual alias with the complete address and ensure the domain is classified as a virtual alias domain.
Outbound delivery is deferred or rejected
Inspect the mail log and the remote server’s response. Check the VPS provider’s port 25 policy, DNS and reverse DNS, firewall rules, sending-IP reputation, and the destination provider’s feedback. If direct delivery is unsuitable for the network or recipient policies, route outbound mail through an authenticated or otherwise approved SMTP relay.
Unexpected forwarding or abuse
Review every catch-all and explicit mapping, then inspect mynetworks, relay_domains, and recipient restrictions. Look for a network range that is broader than intended or a destination that points to another alias and creates recursion.
Messages arrive with the original address in the headers
This is expected. Virtual aliasing changes the envelope recipient used for delivery, but it does not rewrite the message’s To: and related headers. The destination mailbox can therefore show the original domain address even though Postfix delivered the message to a different envelope recipient.
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- Keep a backup of
/etc/postfix/main.cfand the virtual map before changing them. - After each map edit, use the same three-command sequence:
postmap,postfix check, andpostfix reload. - Periodically query important mappings and remove recipients that should no longer receive mail.
- Watch logs for repeated deferrals, loops, authentication failures, and unexpected outbound volume.
- Re-test an unmapped address whenever you add or remove a catch-all.
Keep the text map and its generated database protected with appropriate file permissions, and include both in your backup plan. When changing a destination, test the old and new paths separately so a stale queue or stale map does not obscure the result. If the VPS changes address, revisit reverse DNS, MX records, firewall rules, and any provider relay authorization.
This arrangement keeps the forwarding decision explicit: the domain is recognized as virtual, each intended recipient has a destination, and Postfix’s relay permissions remain separate from alias delivery.
Frequently Asked Questions
Can Postfix forward my domain mail to Gmail?
Yes. Declare the domain in virtual_alias_domains, map each full address in virtual_alias_maps to its Gmail destination, run postmap, and reload Postfix. Gmail or another provider may still defer or reject mail based on the VPS IP, DNS, reputation, and message policy.
Why do I get “relay access denied”?
Check that the domain is listed in virtual_alias_domains and is not also listed in mydestination or relay_domains. Then rebuild the configured map and reload Postfix.
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Not for normal virtual-domain forwarding. /etc/aliases handles local recipients, while virtual_alias_maps matches complete addresses such as [email protected] and can redirect them to remote destinations.
Why did changing the virtual file do nothing?
The indexed database must be rebuilt after edits. Run postmap against the exact path and map type configured in virtual_alias_maps, run postfix check, and reload.
How can I tell whether a recipient is mapped?
Query the configured database directly, for example postmap -q '[email protected]' hash:/etc/postfix/virtual. Replace hash: with lmdb: when appropriate.
Should I use a catch-all address?
Only for a deliberate use case. A catch-all such as @example.com [email protected] also accepts mistyped and abusive addresses, which can create backscatter and excess forwarding. Test an unmapped address before relying on it.
How do I avoid making the VPS an open relay?
Keep mynetworks limited to localhost and explicitly authorized systems, review relay_domains and recipient restrictions, and test from an external account that is not in a trusted network. The host should accept its declared virtual domain without forwarding arbitrary mail for strangers.
Is direct delivery better than an SMTP relay?
Neither is universally better. Direct delivery gives control over the sending IP and fewer third-party dependencies but requires suitable reverse DNS, port-25 access, reputation management, and queue monitoring. A relay can provide approved authenticated submission and share delivery infrastructure, but may impose fees, limits, and service dependence.
The Bottom Line
For reliable Postfix forwarding, classify the domain as a virtual alias domain, map complete recipient addresses, compile the map with the matching database type, and reload after every edit. Point MX to the right host, verify outbound SMTP conditions, keep trusted networks narrow, and test both mapped and unmapped recipients before putting the address into regular use.
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