Problem Sending Email In Phpbb

[smallstonefan]

My board has been running fine for months, then all of a sudden over the weekend users get the following error when posting (the board is trying to send a notification):

 

>Ran into problems sending Mail. Response: 550 Sender verify failed
[B]DEBUG MODE[/B]
Line : 164
File : /home/ivlqvetw/public_html/forums/includes/smtp.php

 

I'm still receiving on the account that is being used, so the account seems to be fine. Nothing was changed on the board or in my configuration - it just stopped working.

 

I would appreciate any guidance you can provide,

[TCH-Thomas]

Sorry I dont know the answer but moving for organization.