Common Sending Errors and How to Fix Them

It is frustrating when email fails. Here are the most common error codes and how to fix them.

1. Authentication Failed (535)

• Error: 535 Authentication failed or Username and Password not accepted.
• Cause: You entered the wrong password.
• Fix:
  • Are you using the Mailbox password? (Not your account login).
  • Are you using the full email (alice@domain.com) as the username?
  • Try resetting the password in the dashboard.

2. Relay Access Denied (554)

• Error: 554 5.7.1 : Relay access denied.
• Cause: You are trying to send without authentication.
• Fix: Ensure your email client has "Authentication Required" checked in SMTP settings. We do not allow unauthenticated open relaying.

3. Daily Limit Exceeded (550)

• Error: 550 User has exceeded sending limit.
• Cause: You hit the 24-hour limit for your plan.
• Fix: Upgrade your plan or wait 24 hours. See Limits.

4. Connection Timed Out

• Error: Could not connect to SMTP host.
• Cause: Your firewall or ISP is blocking usage of port 25 or 465.
• Fix: Try using port 587 (STARTTLS). It is less likely to be blocked by residential ISPs.

5. SPF/DKIM Validation Failed

• Error: Gmail bounces with 550-5.7.26 This message does not have authentication information.
• Cause: Your DNS is not set up correctly.
• Fix: Go to Domains and ensure your status is Active. You cannot send mail if DNS is broken.

6. Email Verification Required (550)

• Error: 550 Sending blocked — verify your email address or a dashboard banner saying "Sending blocked."
• Cause: Your account email has not been verified and the 7-day grace period has expired.
• Fix: Check your inbox for the verification email (sent when you registered or changed your email). Click the verification link. If you can't find it, click Resend verification email in the dashboard banner. Once verified, sending is restored immediately.

7. Recipient Filtered — Invalid Domain

• Error: Message sent via API appears queued but recipient count is lower, or broadcast recipient shows status skipped with reason "Recipient domain has no valid MX records."
• Cause: The recipient's email domain does not have valid MX or A DNS records, meaning it cannot receive email. TrekMail filters these recipients before sending to protect your bounce rate.
• Fix: Verify the recipient email address is correct. If the domain recently changed DNS, wait up to 15 minutes for the validation cache to expire and try again.

8. Recipient Suppressed — Previous Bounce

• Error: Recipient shows as failed with reason "Recipient suppressed due to previous hard bounces."
• Cause: A previous email to this address hard-bounced (the mailbox does not exist or permanently rejects mail). TrekMail automatically suppresses these addresses.
• Fix: Confirm the email address is correct and active. If the recipient has fixed their mailbox, contact support to remove the suppression.