Common SMTP errors and how to solve them

Can’t send your Email Drip Campaign because of SMTP error?

Let’s get familiar with the most common SMTP error messages and a recommended course of action for each of them.

1. Gmail/Google Workspace SMTP
2. Outlook SMTP

Gmail/Google Workspace SMTP

  • 530, “5.5.1”, Authentication Required.
  • 535, “5.7.1”, Username and Password not accepted.

Even though your Username and Password are correct, you may get an authorization error due to Google’s security requirements. In this case, we recommend using an App Password to grant access to your Gmail and set up a connection.

Learn how to connect your Gmail via SMTP and avoid authorization errors.

smtp error


  • 550, “5.4.5”, Daily sending quota exceeded.  

When you get this type of error, it means you’ve reached the number of emails you can send per day according to Gmail’s limits

After reaching the limit, please wait for up to 24 hours before your Gmail’s daily quota is reset. 

To reactivate your email campaign, click “I have resolved the problem. Try sending the campaign again.” on your email account page.  

smtp error


  • Invalid token

This type of error occurs when your Gmail account’s token expires and therefore email account connection is interrupted.

In your account, you will see the following message:

gmail error

To solve the issue, go to your Account Settings on the email accounts page and click the Re-connect Account button.

gmail reconnect

Outlook SMTP

1) 550 5.7.1: Message rejected as spam by Content Filtering
2) 550 5.4.1 Recipient address rejected: Access denied. 

When you get these types of errors, it means that the message could not be delivered for policy reasons—typically a spam filter, receiving domain policy, user preference or the use of anti-spam software on the recipient end.

Learn how to avoid spam filters and increase your email deliverability in our blog articles. 

If you have any questions, please reach out to us and we will gladly help you!

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