Some Emails not making it to destination

Hello,

My emails are not making it to a particular address. Some go but most do not. This started on Friday, Feb 5, 2021. The messages appear to be sent, but they are not received on the other end, and they do not bounce back. Some make it through, but most don't. The IT person at this organization has looked into the issue and said it's not a problem on their end.

As a work around, I have been emailing this address from my yahoo account. All the emails from yahoo make it through, but if I am emailing from my comcast account and cc my yahoo account when emailing this particular address, and messages don't make it to my client's address also don't make it to my yahoo account.

 After reading through some forums with similar issues, I am concerned that maybe some of my emails are being blocked by the servers because spammers have used my email address. I have been helped by the forums in the past, so hoping someone on the comcast team will be able to help. I did send a PM earlier today, but haven't heard anything.