Second this, I've been using them for a couple of years and the service is rock solid.

Third this. I use it for my personal vps'/vms/etc. email sending and liked it so much I replaced o365 send for machine accounts at work with it and it's been sending 30k emails a month to my o365 domain (mostly reports programatically sent from one program/excel sheet [yah I know, don't judge us, it works] to one or a set of users who have 0365 email accounts on my work domain) with no trouble for over a year now. I pay as I go on that account but it's usually 17-25 dollars a month, way less than what I was paying when I had a smaller subset of current senders on o365 and with way less pain because it supports less annoying for programming methods of authentication without having to whitelist ips, which was often impossible because people moved their laptops around and sent from different locations.