At my last job at an email security provider, this was a huge pain in the ass. We would provision new mail servers, and because the new servers' IP reputation t

At my last job at an email security provider, this was a huge pain in the ass. We would provision new mail servers, and because the new servers' IP reputation to Office365, Google, etc. was poor initially, someone (until it became a shell script) had to spend the better part of a week taking the new server out of rotation, putting it back in, and so forth, so not too many of our client's emails got stuck in the new server's reputation blackhole. I was there for 10 years, and this was only a problem in the final ~2 years of my employment, which roughly lines up with your 4 years remark.