SMTP Issues

Hello – I have all of a sudden had issues sending out emails with smtp. That plugin will not help me unless i upgrade. It has worked all along for months, and now I get the error message

Email Source: WP Core
Mailer: Other SMTP
SMTP Error: Could not authenticate.

What could be the issue if I have not changed my password at all? I just changed my email password again to see if that was the issue but this was not the issue.