Emails (still) being blocked from 800-Pet-Meds

Hello, my pet supply vendor 1-800-PetMeds informed me yesterday that Comcast is blocking their outgoing emails.  This appears to have been happening since September.  Why is that?  I use them very frequently and now I can't get order confirmations and status from them. 

I saw a post from early November that spoke to the same issue and was noted as being resolved, but I was updated from Pet-Meds just yesterday 12/3/20.

Their address is CustomerService@1800petmeds.com.  Please let me know?  Thank you.