Emails becoming undeliverable

This is very confusing to me why this has just started happening. I installed the Postman SMTP plugin on https://sloworkforce.com about 3 months ago using the Google API with a forwarding email on our hosted domain (GoDaddy). I can send test emails all day to a qualified email address but not to a hosted forwarding email address. As of today, I cannot reference a simple GoDaddy forwarding email ([email protected]) with Contact Form 7 as the “To” or it will return the following error:

Delivery to the following recipient failed permanently (ip address commented out):

[email protected]

Technical details of permanent failure:
Google tried to deliver your message, but it was rejected by the server for the recipient domain sloworkforce.com by smtp.secureserver.net. [xx.xxx.xxx.xx].

The error that the other server returned was:
550 5.1.1 <[email protected]> Recipient not found. <https://x.co/irbounce&gt;

I have had this forwarding email on the site for over 9 years and not sure if it’s a GoDaddy issue or what exactly. Consequently, I have had to hard code the forwarding email address in the Contact Form 7 form instead of relying on the hosted forwarding address. Interestingly, my other website is also hosted by GoDaddy using the same techniques as this site and it can handle 7 different forwarding email addresses without burping up an email delivery failure. Suggestions?

https://www.ads-software.com/plugins/postman-smtp/