First identify who rejected the message
A 550 relay rejection has two different starting points. If another mail server tried to deliver a message to your domain and the intended DirectAdmin mail server rejected the recipient, check whether DirectAdmin is meant to treat that domain as local. If your own mail application received the error while trying to send to an outside address, check its authenticated submission settings instead. The words “authentication required” alone do not tell you which route failed.
Use this guide only for a service that actually includes DirectAdmin mail. A website hosted in DirectAdmin may still use an external mail provider. Do not change MX, the Local Mail Server option or SMTP authentication until you know which server rejected which recipient. A 550 reply means that SMTP transaction was refused; it does not identify the underlying cause without the route and context.
Read the bounce or client error as a route map
Capture the rejecting server name, recipient domain, timestamp with time zone, exact reply and the SMTP stage if shown. Redact personal addresses and message content before sharing evidence. A bounce saying “in reply to RCPT TO” shows where the recipient was refused. Compare these patterns:
Outside sender bounced by the intended mailbox server
First check the public MX, intended mailbox location and DirectAdmin local mail routing. The mail-service operator or authorised DirectAdmin account owner can act on those settings.
Your own mail application cannot send to an outside domain
Check its configured outgoing server, authentication identity and supported TLS mode. The mailbox and device owner should review the client settings, then involve the submission-service operator if needed.
Bounce from a different receiving provider
Check that provider’s actual rejection and recipient policy. The receiving provider or recipient-domain owner can investigate it.
RFC 6409 separates user message submission from server-to-server transfer. Treating a receiving server as an open relay is not a safe fix for either problem.
Check where the domain is supposed to receive mail
Confirm the intended mail provider from the accepted service and the domain owner. Check the public MX answer with dig MX example.com +noall +answer, then compare it with the provider’s documented target and the hostname in the bounce. Use the authoritative DNS guide if the public answer differs from a panel display. MX tells other servers where to try delivery; it does not prove that the receiving server recognises the domain as local or that a mailbox exists.
If mail is intentionally hosted by Microsoft 365, Google Workspace or another external provider, leave DirectAdmin’s local-mail handling disabled unless a separately designed split-delivery route requires it. DirectAdmin documents the remote-mail setup as a separate Local Mail Server and MX decision. Turning local handling on simply to remove the 550 response can divert messages away from the intended external service. If the public MX itself is wrong, coordinate a controlled MX correction; do not alter it on the strength of one error string.
If DirectAdmin should receive mail for this domain
When the rejecting DirectAdmin server really is the intended recipient host, check the domain’s mail-routing control in its DirectAdmin account. Depending on the enabled interface, the MX Records area exposes a Local Mail Server option. Confirm that the required mailbox, alias or forwarder exists and that the domain belongs to the correct account. Do not toggle the option during a mail migration without listing the current addresses and recording the intended route.
DirectAdmin’s Exim troubleshooting documentation says this exact response can occur when Exim does not consider a recipient domain local. The operator can compare the panel’s setting with the server’s local-domain state, including /etc/virtual/domains, and inspect the time-matched Exim rejection. A customer without server administration rights should ask the operator to do this; editing a server file directly is not a general account-level fix and may conflict with managed configuration. After the authorised correction, ask an external sender you control to send one new, non-sensitive message. Confirm server acceptance and actual mailbox arrival, including the Spam folder, before declaring recovery.
If your own mail client cannot submit a message
Check the outgoing server configured for that account, its full username, authorised From address, authentication method and encrypted connection against the actual mailbox provider’s instructions. DirectAdmin gives examples using authenticated SMTP submission, but the correct hostname and available ports depend on your service. Do not assume that a generic example is a Novasean-wide endpoint or entitlement. An incoming IMAP login can work while the separate outgoing SMTP configuration fails.
Test one harmless message to an outside address you control. If the provider accepts it but a later remote server rejects it, use the remote rejection instead of changing the client again. Follow the broader outgoing-mail diagnosis for submission, queue and remote-delivery branches. Never disable TLS validation or allow unauthenticated relaying to suppress the error.
Escalate with enough evidence to protect mail delivery
Give support the affected domain, whether the failed message was incoming or a client submission, the redacted recipient, the rejecting hostname, exact 550 text, timestamp and public MX result. State which provider is meant to host the mailbox. Do not include a password, complete message body or unrestricted server log. For a managed service, the operator owns server routing and Exim changes; for a self-managed server, only an authorised administrator should perform them.
Should I change SPF, DKIM or DMARC? Not for this error alone. First determine which server refused the recipient or submission. Mail authentication has separate failure messages and evidence.
Does switching Local Mail Server on always fix 550? No. It is appropriate only when this DirectAdmin server is meant to accept that domain’s mail and the authorised operator has checked the route. An external-mail domain needs its planned remote route.
Will correcting MX alone fix a local-domain mismatch? Not necessarily. MX changes the public destination, while Exim’s local-domain classification is a separate server setting. Verify both, then repeat an external delivery test.
Sources and technical references
Related guides
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