Mailu + SMTP Relay Guide

Recommended settings for mailboxes, transactional relay, and clean DNS.

Mail hosting

Recommended structure

Mailu and SMTP Relay solve different problems and work best together.

  • Mailu hosts mailboxes, aliases, and webmail for your team.
  • SMTP Relay sends transactional mail from apps, notifications, and forms.
  • Separating the traffic keeps sending reputation more stable.
  • DNS should be aligned from day one: MX, SPF, DKIM, DMARC, and rDNS.
SMTP relay

Mailu for inboxes

Use Mailu when you need solid control over mailboxes and your own domains.

  • Mailboxes on your domain with aliases and forwarding.
  • Webmail, IMAP, and POP3 access for staff and customers.
  • Centralized password and anti-spam policies.
  • A good migration target from cPanel or Google Workspace.
DNS

DNS checklist

These records are the baseline for deliverability and alignment.

  • MX pointing to the Mailu host for inbound mail.
  • SPF authorizing the actual IP or relay used for sending.
  • DKIM enabled for the visible sender domain.
  • DMARC starting at p=none, then raised gradually to quarantine or reject.
  • The sending IP should have a PTR / rDNS hostname that matches the relay identity.
Reference example
example.com.        MX   10  mail.example.com.
mail.example.com.   A    203.0.113.10
example.com.        TXT  "v=spf1 mx ip4:203.0.113.10 -all"
mail._domainkey.example.com. TXT "v=DKIM1; k=rsa; p=..."
_dmarc.example.com. TXT "v=DMARC1; p=none; rua=mailto:[email protected]"

When to use what

Simple rule: Mailu for people, relay for software.

  • Mailu for team inboxes, aliases, and webmail.
  • SMTP Relay for ERP, websites, notifications, and automated flows.
  • Use both together if you want a complete email platform.
  • Keep transactional traffic separate from the team inbox.

Recommended structure

Mailu and SMTP Relay solve different problems and work best together.

  • Mailu hosts mailboxes, aliases, and webmail for your team.
  • SMTP Relay sends transactional mail from apps, notifications, and forms.
  • Separating the traffic keeps sending reputation more stable.
  • DNS should be aligned from day one: MX, SPF, DKIM, DMARC, and rDNS.

SMTP Relay for applications

Use the relay for messages sent by apps, portals, and automations.

  • Common ports: 587 for submission, 465 for SMTPS, and 2525 as a fallback.
  • Dedicated SMTP auth with TLS required in production.
  • Dedicated IP or controlled pool for reputation and volume.
  • Ideal for billing, notifications, and system alerts.

Recommended settings for mailboxes, transactional relay, and clean DNS.