Using Email Address Formats as Usernames for SMTP Authentication

Summary: This article explains how to configure systems that require email address formats for usernames when using DuoCircle's SMTP services. This method is specifically for SMTP sending and does not apply to our Outbound API.


This solution is applicable only for SMTP sending services and is not supported for Outbound API usage.


Some applications require usernames to be in the format of an email address, which may not align with the standard formatting of DuoCircle credentials.


For systems that require an email address format for the username, users can append to their regular DuoCircle username. This modification allows the application to recognize the username as an email address.

Steps to Implement:

  1. Modify Username: Add to your existing DuoCircle username.
    Example: If your original username is user123, modify it to
  2. Authentication Process: During the SMTP authentication process, the suffix will be automatically removed from the username before checking for authentication. This ensures that the authentication process remains secure and effective, while accommodating the format requirement.

Note: This solution only works for SMTP sending. It does not apply to our Outbound API (, where usernames must adhere to the standard formatting specified for API usage.


Using the method described above, systems requiring an email-formatted username can effectively integrate with DuoCircle’s SMTP services, ensuring compatibility and functionality.


For further assistance or if you encounter any issues, please contact our support team