Email-Based 2FA Fails Due to SMTP Rate Limit (450 username ratelimit exceeded)

Original Question or Issue:

Users were unable to complete email-based 2FA authentication when signing in to FileCloud Online. The system initially indicated that the 2FA email was being sent, but the request then failed with an error. The issue affected multiple user accounts.

Environment:

• Product - FileCloud Online
• Version - 23.262
• Platform - Linux

Steps to Reproduce:

1. Log in to FileCloud Online using an account configured for email-based 2FA.
2. Enter the user's credentials.
3. FileCloud attempts to send the 2FA verification code via email.
4. The interface initially indicates that the email is being sent.
5. The request then fails and displays an error.
6. Reproduce the issue with multiple accounts configured for email-based 2FA.

Error or Log Message:

Email Send Failed SMTP Error: data not accepted.
SMTP server error: DATA command failed
Detail: username ratelimit exceeded
SMTP code: 450

Defect or Enhancement Number:

 No JIRA assigned 

Cause:

The FileCloud Online SMTP service was rate-limiting the customer's SMTP email sending account.

The SMTP server returned a 450 temporary rejection with the detail:

username ratelimit exceeded

Because the same SMTP service is used to send production emails, the rate limit also prevented FileCloud from delivering email-based 2FA codes to users.

The issue affected multiple accounts because the limitation was at the SMTP sending/account level rather than being isolated to an individual FileCloud user.

Resolution or Workaround:

The issue was escalated to the FileCloud OnlineOps team.

OnlineOps increased the email sending limit for the customer's environment to unlimited.

The customer subsequently confirmed that the issue was resolved and requested to close the case.

Notes: