I use MIAB on Vultr and it’s working pretty good, but even with Port 25 open, there’s at least one ISP that’s blocking my IP address for mail connections. EDIT: That one ISP has unblocked me. Dunno if it’s because I sent a request to their abuse department, or it was a temporary block.
I have yet to see a list of VPS providers with good IP address reputation for hosting mail servers. I’m not surprised there’s this much trouble, considering how pervasive spam is.
I used Linode before and was quite happy, but I switched to Vultr to get more for my money. This may have been before Linode had the $5 plan for a 1GB server.