Has something changed by default that I can change back to how it was prior to the last few weeks? (I am not technically inclined, to be clear.)

Numerous emails have been bounced by Zoho, my main email account. The notifications I get from Simple Login indicate it's a Zoho issue. I've been corresponding with Zoho, who state they don't even see bounced emails on their end. I never had an issue prior to a few weeks ago - emails would go through fine. Zoho has requested relay logs from the sending server to delve into the problem further?

So, since I was not getting important banking notifications, I decided to switch my aliases to go to my Mailfence account. Same issue - getting notifications that Mailfence is bouncing the forwarded email aliases. Didn't have that issue in the past with them either, when it was my main email.

Long explanation to ask - has something been changed in accounts by default, and, if so, how do I change it back?

Thank you - appreciate any assistance before I decide to just ditch what worked so well!