This morning, one of my comcast email accounts began rejecting emails sent by Pegasus
{WinPMail version: Version 4.80.1028, Jan 16 2022, build ID 1028
IERRenderer 2.6.6.0}.

Error Message: "550 5.1.0 Please ensure your email address and authenticating user match when sending."

In discussion with Comcast Tech support (yes, you can get through to them if you hold your tongue right) we determined:

1 - it only effects one of my Comcast email accounts (the other one I use only rarely - it's my contact account for my own servers - it still functions)

2 - It's only if I try to access that account via Pegasus for sending email - I can use Comcast's webmail interface fine.

3 - I can retrieve email from that sending-blocked account using Pegasus.

4 - I have changed nothing with regards to this account set up or configuration on Comcast or Pegasus for at least 5 years - last change involved new "ports" (465/995) for security.

Comcast Tech support reports that it is indeed OLATH-2 related, and suggested they are going to try to "copy" the configuration "from the one account I mentioned that still works over to the account that is failing, since I am an authenticated customer account."

"They will call me back in an hour or so.."

Stay tooned.. smile