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To run email from a VPS, install Postfix as the mail-transfer agent, configure a real hostname and tightly scoped relay policy, then add Dovecot only if users need mailbox access or SMTP authentication. Finish with TLS, DNS sender authorization, protocol tests and ongoing abuse monitoring. Installing Postfix alone does not make mail trustworthy or guarantee inbox delivery.
What you are building
An email server has separate jobs. Postfix transfers messages between servers and accepts mail for the domains you configure. Dovecot can provide IMAP or POP mailbox access and a SASL authentication service that Postfix uses for SMTP-AUTH. You may run Postfix without Dovecot when the VPS only sends system mail or forwards mail elsewhere; you need Dovecot when people must authenticate to submit mail or read local mailboxes.
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The setup below assumes an Ubuntu VPS with a static public IPv4 address, a domain whose DNS zone you control, and a provider that permits mail traffic. Provider rules for port 25, reverse DNS and abuse response differ, so verify those policies before changing DNS or deploying.
Prerequisites and identity checks
Collect these values before installing packages:
- A fully qualified mail hostname, for example
mail.example.com. - The domain or domains the server will accept mail for, such as
example.com. - The VPS public IP address and the provider’s reverse-DNS setting.
- The network ranges that are genuinely trusted to relay through this host.
- The mailbox format you want (for example, Maildir or mbox) and the local users who will own mailboxes.
- A TLS certificate whose name matches the SMTP hostname, including the issuing chain required by clients.
Make forward DNS, reverse DNS, the operating-system hostname and the certificate name agree. A mismatch does not automatically block every message, but it makes troubleshooting, authentication and recipient trust harder.
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Install Postfix on Ubuntu
-
Update package metadata and install Postfix:
sudo apt update sudo apt install postfix -
When the package asks for a configuration type, select Internet Site if this VPS will deliver mail directly. Ubuntu’s mail-service guidance recommends deciding the accepted domain, server network range, local username and mailbox format before completing configuration.
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Enter the system mail name when prompted. You can refine the values later in
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Ubuntu identifies Postfix as its default supported mail-transfer agent. The package normally starts the service after installation; check its state before making changes:
sudo systemctl status postfix
sudo postfix checkSet the core Postfix policy
Edit /etc/postfix/main.cf and set the identity, destinations and trust boundaries. A minimal pattern looks like this; replace the example names and networks with your own values.
myhostname = mail.example.com
mydomain = example.com
myorigin = $mydomain
inet_interfaces = all
inet_protocols = all
mydestination = $myhostname, localhost.$mydomain, localhost, $mydomain
mynetworks = 127.0.0.0/8 [::1]/128
home_mailbox = Maildir/
myhostname and accepted destinations
myhostname should be the host’s canonical mail name. mydestination lists names for which this server is final delivery. Include only domains and hostnames that belong on this VPS. Adding a domain accidentally can make the server accept mail it cannot deliver correctly; omitting a domain causes legitimate local recipients to be rejected or relayed elsewhere.
mynetworks and relay restrictions
mynetworks is the trusted-network list. Keep it narrow: loopback addresses and explicitly controlled private networks are typical entries. Never use a broad public range merely to make a client work. An open relay lets unauthenticated outsiders send to arbitrary destinations, quickly damaging the IP’s reputation and triggering provider abuse action.
Postfix should reject unauthenticated attempts to relay mail for destinations outside your local domains. A commonly used restriction is:
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smtpd_relay_restrictions = permit_mynetworks, permit_sasl_authenticated, reject_unauth_destinationThe important behavior is the order: trusted local clients and authenticated users may relay; every other client is rejected when the destination is not local. Reload after validating the file:
sudo postfix check
sudo systemctl reload postfixMailbox format and local delivery
With home_mailbox = Maildir/, each user’s messages are stored below a Maildir directory in that user’s home directory. If you choose another format, configure Dovecot to read the same location. A mismatch between Postfix’s delivery path and Dovecot’s mail location produces an apparently empty inbox even though delivery succeeds.
Add Dovecot for mailbox access and SMTP authentication
Install the core Dovecot package when clients must authenticate or retrieve local mail:
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Expose the Postfix SASL socket
Configure Dovecot’s auth service to create a socket in Postfix’s private directory, with ownership and permissions that let Postfix access it. A typical configuration fragment is:
service auth {
unix_listener /var/spool/postfix/private/auth {
mode = 0660
user = postfix
group = postfix
}
}
In Postfix, point SASL at that socket and disable anonymous authentication:
smtpd_sasl_type = dovecot
smtpd_sasl_path = private/auth
smtpd_sasl_auth_enable = yes
smtpd_sasl_security_options = noanonymous
smtpd_sasl_local_domain = $myhostname
Use authentication mechanisms that are protected by TLS. Do not expose credentials over an unencrypted connection. After editing, restart Dovecot and reload Postfix:
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sudo systemctl restart dovecot
sudo postfix check
sudo systemctl reload postfixChoose the client submission path
Authenticated users should submit through a dedicated submission service rather than relying on unrestricted port 25 behavior. Enable the submission service in Postfix’s master.cf, require SASL authentication there, and require TLS before accepting credentials. Your mail clients must be given the hostname, username, password and the submission port selected by your configuration. Keep port 25 available for server-to-server SMTP, while applying a stricter policy to authenticated client submission.
Create local Unix accounts only for people who should receive mail. Protect passwords, use a supported password database and remove unused accounts. Dovecot authentication is an access-control boundary, not a substitute for TLS.
Configure TLS correctly
Obtain a certificate for mail.example.com and configure Postfix’s certificate, private-key and chain files. Postfix’s TLS documentation requires the server certificate to be presented with the issuing chain in the required order. Protect the private key so only the mail service and administrators can read it.
smtpd_tls_cert_file = /etc/ssl/mail/fullchain.pem
smtpd_tls_key_file = /etc/ssl/mail/privkey.pem
smtpd_tls_security_level = may
smtpd_tls_auth_only = yes
smtpd_tls_auth_only = yes prevents SMTP authentication until TLS is active. The server-side security level shown here allows opportunistic encryption for ordinary SMTP while still advertising STARTTLS. Whether outbound encryption should be opportunistic or enforced depends on the recipient environment: strict enforcement can protect confidentiality but may prevent delivery to domains that do not support the required TLS policy.
When you renew a certificate, reload Postfix and test the presented chain. Also configure TLS for Dovecot’s IMAP or POP services if those services are enabled; SMTP TLS does not automatically secure mailbox retrieval.
Publish DNS records for identity and authorization
Mail-host address records
Create an A record for the mail hostname that points to the VPS address. If you use IPv6, publish an AAAA record only when the server is correctly configured for IPv6 and the provider’s reverse DNS is in place. A hostname that resolves to an address unable to send mail creates intermittent failures.
Reverse DNS
Ask the VPS provider to set the public IP’s PTR record to the same mail hostname, then confirm that the hostname resolves forward to that address. Reverse-DNS control usually belongs to the provider rather than the domain registrar.
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SPF
SPF is a DNS policy that lists the systems authorized to send mail for a domain. Publish one SPF policy that matches the actual sending path. If this VPS sends directly, authorize its public address; if another service also sends mail, include that service according to its documented SPF mechanism. Multiple independent SPF records are invalid, and an outdated record can cause recipients to treat legitimate messages as suspicious.
Additional sender-authentication records
Recipients may also expect DKIM signatures and a DMARC policy. These are separate from Postfix transport and are not created merely by installing Dovecot. Add them only after deciding which system will sign messages and which reports or enforcement policy your domain can handle. Align the visible From domain with the authenticated sending domain where your recipient policy requires it.
Test SMTP at the protocol level
Test locally first, then from a network that represents a real client. A basic SMTP conversation can confirm that the service advertises the capabilities you expect:
telnet mail.example.com 25
ehlo mail.example.comThe response should include a 250-STARTTLS capability when TLS is enabled. On the authenticated submission service, verify that 250-AUTH appears only where you intend to offer authentication. Do not send a real password through an unencrypted Telnet session. Use a TLS-capable SMTP client to test login and message submission.
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Confirm DNS answers:
dig +short A mail.example.com dig +short MX example.com dig +short TXT example.com -
Inspect the certificate and STARTTLS negotiation with a TLS-capable client. Verify the certificate name, expiration and complete chain.
-
Send a test message to an account you control and inspect both the SMTP response and the recipient’s authentication results.
-
Watch the mail log while testing:
sudo journalctl -u postfix -f sudo journalctl -u dovecot -f -
Check the queue when delivery is delayed:
mailq sudo postqueue -p
A successful SMTP 250 response means the next server accepted responsibility; it is not proof that the message reached the inbox. Continue by checking queue status, bounce notices and the recipient’s headers.
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Troubleshoot the common failure modes
Port 25 is blocked
Some VPS providers block outbound port 25 for new or unverified accounts. Request removal of the restriction or use a permitted SMTP relay. Do not assume a local configuration change can bypass a provider-level block.
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Check that Dovecot is running, the Postfix private/auth socket exists, its ownership permits Postfix access, and smtpd_sasl_path matches the socket path. Confirm that the submission service has SASL enabled and that the client is using the intended hostname and TLS mode. Logs from both services usually identify whether the failure is a socket, password or policy problem.
Messages are rejected as relaying denied
Verify that the recipient domain is in mydestination when it is local, or that the sender authenticated successfully for an external destination. Do not solve the error by adding every network to mynetworks; that creates an open relay.
Mail is deferred or remains queued
Read the per-message log entry for the remote server’s response. DNS failures, connection timeouts, TLS negotiation errors, provider blocks and temporary recipient throttling require different fixes. Correct the underlying issue, then let Postfix retry or use the queue-management commands deliberately.
Messages go to spam
Inbox placement is not guaranteed by Postfix. Check forward and reverse DNS, certificate naming, SPF and any DKIM or DMARC requirements used by your recipients. Review bounce and rejection logs, send consistent traffic, suppress abusive or invalid recipients, patch the VPS and investigate whether the IP has a poor reputation. A new or shared VPS address may need the provider’s help if it is already listed or has a history of abuse.
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- Apply Ubuntu and mail-software security updates promptly.
- Restrict SSH, Postfix administration and Dovecot management to trusted administrators.
- Use firewall rules that expose only the SMTP and mailbox protocols you actually provide.
- Require TLS for authenticated submission and protect private keys, password databases and backup copies.
- Monitor queue length, deferred mail, authentication failures and rejection trends.
- Set rate limits and alerting appropriate to your users so a stolen password cannot generate an uncontrolled burst.
- Keep abuse contacts and a recovery plan; providers may suspend an IP when recipients report unsolicited mail.
- Back up mailbox data and configuration, but never restore secrets or private keys to an untrusted host.
Direct delivery or an SMTP relay?
Running Postfix as a direct sender gives you control over message data, configuration and the sending path. It also makes you responsible for DNS, reputation, queue management, abuse handling, TLS, patching and delivery troubleshooting. An SMTP relay can reduce infrastructure work and may provide delivery monitoring, but it introduces a third party, recurring cost and its own sending limits and policy requirements.
| Decision factor | Direct Postfix delivery | SMTP relay |
|---|---|---|
| Data and configuration control | Highest control on your VPS | Shared with the relay operator |
| Sender reputation | You build and protect the VPS IP reputation | Depends on the relay’s pools and policies |
| Deliverability monitoring | You must build log, queue and bounce monitoring | Often supplied as part of the service |
| Port and reverse-DNS policy | You must satisfy the VPS provider | The relay handles its own sending infrastructure |
| Recurring cost | VPS and operational labor | Relay fees plus any VPS components |
| Operational workload | Patch, secure and troubleshoot the complete mail stack | Maintain the client integration and account policy |
| SPF, DKIM and DMARC | You configure records and signing for your path | Follow the relay’s authorization and signing instructions |
Choose direct delivery when you need control and can actively operate an Internet-facing mail system. Choose a relay when predictable delivery support and lower operational burden matter more than keeping the entire sending path on your VPS. In either case, authenticate clients, publish accurate DNS and prevent unauthorized relaying.
Quick Recap
Final deployment checklist
- Confirm the static IP, provider mail policy, hostname and reverse DNS.
- Install Postfix and select Internet Site only when the VPS is intended to deliver mail directly.
- Set
myhostname, accepted destinations, a narrowmynetworkslist and a consistent mailbox format. - Verify that unauthenticated clients cannot relay to arbitrary external domains.
- Install Dovecot only when mailbox access or SMTP-AUTH is required, then connect its SASL socket to Postfix.
- Configure a certificate and complete chain for the SMTP hostname; require TLS before authentication.
- Publish address, reverse-DNS, MX and SPF records, plus DKIM or DMARC records required by your chosen mail flow.
- Use EHLO to verify STARTTLS and AUTH on the intended service, then test an authenticated message with a real TLS-capable client.
- Inspect logs, queue state and recipient authentication results.
- Continue patching, monitoring abuse and reviewing deliverability after launch.
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