How to pause throttling and blocking of out-of-date on-premises Exchange Servers

ManRenas Exchange 2013 is out-of-support and entirely non-compliant. If you plan to continue connecting to EXO using Exchange you must replace the 2013 server with a 2016 or 2019 server (both versions are still in-support and thus compliant) with the latest CU and SU. The report in the EAC Details column for the server(s) will show you which Exchange 2016 and 2019 builds qualify. If you haven't done so already, be sure to create an enforcement pause (via the report UI or via PowerShell) for up to 90 days. Also note that enforcement starts with a 30-day Reporting Only stage. So effectively you get 120 days this year free from throttling or blocking.

RyanM If your connecting servers are indeed up to date, then I suspect the throttling is due to something else (e.g. suspicious behavior / excess volume or bad sender detected) and NOT related to enforcement for out-of-date servers. You can check the SMTP error codes you see in your on-prem logs - 450 4.7.230 (temp reject) or 550 5.7.230 (perm reject / block) errors are the ones we generate when the issue is an out-of-date server.