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.

See also

• Checking DNS Status
• Bring Your Own SMTP