I still run my own server and do not use a relay service and do host on a cheap (free actually, OCI) VPS and other cheap VPS's before that since the 1990's. In that time only one big email service blocked my IP by a large block range, twice...Microsoft but by filing a support request here https://olcsupport.office.com/ both times, they resolved in in less than 2 days. The second incident was just in the last several days so the request does work.