Hosting email isn't just a process. Sure, it's definitely easier when you have _users_ sending mail. When you have _customers_, it gets a tad more complicated.

Hosting email isn't just a process. Sure, it's definitely easier when you have _users_ sending mail. When you have _customers_, it gets a tad more complicated. Sure, you can be a good kid and keep IP's warmed up, set up authentication and make sure DNS is configured properly. None of those help when some spammers decide they like your hosting service and start purchasing accounts with stolen credit cards, nor when you have customers re-using passwords, refusing to use 2FA and so on, and their accounts inevitably get hijacked. Office 365 and Gmail silently dropping mails doesn't make things easier.