Fixing Common Email Sending Errors

An SMTP error is usually a useful clue, not a reason to repeatedly resend the same message. Start with the exact message from the mail app or webmail, then use the matching check below. Never send your mailbox password, SMTP credential, or API token to support.

Quick checks before changing anything

1. In Domains, confirm that the sending domain is Active and has a route selected in SMTP.
2. In the mailbox's Apps & devices screen, copy the exact server, port, encryption, and username for that mailbox.
3. Use the mailbox password in the mail app, not the TrekMail account password.
4. Check the dashboard for an account-verification, billing, rate-limit, or security notice.
5. Send a small test to an address you control after each change.

Authentication failed

What you may see: 535, 5.7.8, “Authentication failed,” or “Username and Password not accepted.”

Usually means: The mailbox address, mailbox password, server, encryption choice, or authentication method is wrong.

What to do:

• Enter the full mailbox address as the username.
• Reset the mailbox password if you cannot confirm it, then update every mail app that uses that mailbox.
• Compare the app's settings with Apps & devices instead of reusing a server name from another account.
• Use password authentication over the encryption shown in the setup screen. Do not select OAuth or a provider-specific method unless the setup screen explicitly asks for it.

Sender or relay not authorized

What you may see: 553, 5.7.1, “relaying denied,” “sender address rejected,” or “sender not authorized.”

Usually means: The message is using a From address that is not authorized for the signed-in mailbox, the domain has no usable sending route, or the external provider has not approved the sender.

What to do:

• Select a verified From address that belongs to the mailbox or a configured Sending address.
• Open the domain's SMTP tab and confirm the route is saved and working.
• If the domain uses a custom profile, complete sender verification with that provider and follow its DNS instructions.
• If the domain is on Nano, add a working custom SMTP profile or move to a paid mail plan for Managed TrekMail SMTP.

The domain is not ready to send

What you may see: “Domain is not verified,” “SMTP is not configured,” or a sending option marked unavailable.

Usually means: DNS is still pending, the domain is deprovisioning, or no route has been selected for the domain.

What to do: Open Domains, compare the required records with the live DNS zone, and wait for the status to become Active. Then select a route in SMTP and send a test message. DNS status and route selection are separate checks; completing one does not automatically complete the other.

A limit was reached

What you may see: a temporary 4.7.1 error, a rate-limit message, or mail that remains deferred.

Usually means: The hourly or daily allowance, new-domain warm-up, or never-paid safety limit has been reached.

What to do: Check the current values in the SMTP tab and dashboard. Count every recipient, reduce the send size, and wait for the indicated limit window before retrying. If the domain is new, use the current warm-up allowance rather than the headline plan limit. See TrekMail Sending Limits by Plan.

Connection or TLS problem

What you may see: “Could not connect,” timeout, connection refused, STARTTLS, SSL, TLS, or certificate errors.

Usually means: The mail app has the wrong host, port, or encryption setting, or the network is blocking the selected port.

What to do: Copy the mailbox's settings from Apps & devices. If the app supports both secure options, use the exact port and security combination displayed there. Try a different trusted network only as a diagnostic step. Do not disable encryption or accept a certificate warning just to make a test send work.

Account email verification, billing, or security block

What you may see: a dashboard banner that sending is blocked, or a message that asks you to verify the account email.

Usually means: The account owner has not completed required email verification, the account's paid entitlement is unavailable, or a security control has paused sending.

What to do: Follow the action in the dashboard. For email verification, use the current verification message or resend control. For a billing problem, resolve it in Billing. If only one mailbox is paused after unusual activity, change that mailbox's password, update its mail apps, and contact support with the error and time of the failed send.

A recipient rejects the message

What you may see: 5.1.1, “user unknown,” “mailbox full,” or a recipient-address rejection.

Usually means: The receiving address is incorrect, no longer exists, is full, or the receiving provider has rejected the message.

What to do: Confirm the address through another trusted channel. Do not keep retrying an address that returns a permanent failure. TrekMail can suppress repeatedly failing recipients to protect delivery; remove or change the address only after confirming that it can receive mail again.

Messages go to spam instead of failing

This is a delivery-quality issue, not an SMTP connection failure. Confirm the domain's DNS records, send only expected mail, keep the recipient list clean, and review bounces and complaints before scaling up. See Emails Go to Spam.

What to include in a support ticket

Include the sending address, recipient domain rather than a recipient's private mailbox when possible, approximate time and time zone, mail app, exact error text, and what changed just before the problem. Exclude passwords, SMTP credentials, tokens, full message bodies, and unnecessary personal data.