Exim Mailman and Retry Rates

Greetings, I am running a server that has cPanel/WHM with Exim and Mailman running fine except for the dreaded Yahoo issue that many others have had. This server is well secured and we follow best practices. The mailman lists are for a school that is fairly busy and sends around 5k emails per month. We have DMARC, SPF and DKIM on these domains as well. I have adjusted retry rules until I am blue in the face. The error I am getting is this: SMTP error from remote mail server after pipelined MAIL FROM: SIZE=9550: 421 4.7.0 [TSS04] Messages from x.x.x.x temporarily deferred due to unexpected volume or user complaints - 4.16.55.1; see