Common causes
- A wrong or expired password or API key.
- Two-factor sign-in is on and an app password is required.
- The sending service disabled the account or key.
- The wrong port or encryption setting makes the login fail.
How to fix it
- Re-enter the credentials and test the login separately.
- Create an app-specific password or a fresh API key if your provider requires one.
- Check the port and the TLS setting in your mail settings.
- Make sure the account is active and not suspended.
Frequently asked questions
Does it affect my list?
No. The message never left your side, so no address was judged. Fix the login and send again.
Where should I store credentials?
In your application's secure settings, never in the page or in code that is shared.