[mailop] AT&T/Yahoo contact or process?

I know AT&T issues were just discussed at length a month ago, though I didn't find another approach to resolve blocklist issues in that thread. We have an IP blocked by AT&T, and no response back to us or multiple customers who wrote, as instructed, to [ mailto:abuse_...@abuse-att.net | abuse_

[mailop] Domain delivery issue sending to Proofpoint?

I am working with a company whose employees are finding that their emails to a number of Proofpoint protected recipients are never arriving. There is no bounce or error, and in almost every case the recipient doesn't receive anything (in one case a recipient found the email in a spam quarantine/