Setting that stuff up is not that hard, you can even just use unix Sendmail. What's hard is actually making sure your emails get delivered and don't end up in

Setting that stuff up is not that hard, you can even just use unix Sendmail. What's hard is actually making sure your emails get delivered and don't end up in the spam folder. Starts with the easy stuff like DMARC (needs DKIM & SPF), goes further to properly warming your IP's, then to properly parsing hundreds of different error response messages and good retry scheduling, and to complex problems like individual mail receivers spam and max-throughput rules. Also these companies sell you the ability to easily make campaigns targeted at a specific subset of your contacts.