Hi David,

Sorry to hear this problem is still present. Please answer the following questions to help me understand your issue:

- Can you still receive email?
- Have you contacted whoever hosts your mailbox to explore whether something has changed on their end?
- Is the sending issue intermittent? Have you been able to send ANY email since this issue began?

The original bounceback error seems to indicate that your email address cannot be authenticated within your account, suggesting there may be an issue with some of the servers associated with the company you are hosted with, OR they have (for some reason) changed their outgoing email settings without informing their customers. Which I doubt.