I was originally going to go with sendgrid but they banned my account the second I registered it, I sent them an email and eventually got in and set up a free account to test with next time i tried to access it their login page got stuck in a redirect loop. Figured that if they're having that much trouble with mastering the simple act of logging into an account and they were putting that much effort into keeping people out that I'd take my custom elsewhere. Moved to mailersend, apart from an incident the first day were they said I was on a warning for a dodgy email subject when the only thing being sent was default xenforo emails it's been fine.