I wish there was enough space here to write out all the things wrong with Sendgrid. The usual stuff with dominant players in any market. Stripe. Google. Microsoft. Too big to care.
Multiple account blocks with no warning, no questions, over weekends when no one sees it. False positives triggering automated actions from their loosey string-matching for at-best guesswork bad URLs. No recourse. No communication. Dark(est) patterns to try and contact support. Or just no support. No response. Repeated global blocks for the same exact reason that was already solved.
Here's my favorite example: There is a massive service called Formaloo, which is exactly what it sounds like: a copy-cat of Google Forms, Microsoft Forms, every other generic form-builder service. One of our customers included their Formaloo link, which opens a quick "exit interview questions for graduating students from a private middle school". We send 60,000 emails per day and have a 99% reputation IN Sendgrid for 10+ years. With no warning, Sendgrid blocks our entire account because the word "formaloo" can be used for spam. So for 4 days with absolutely no communication, no response, no indication which specific email was at fault. We called, we emailed, we tried chat, we emailed more, we responded to tickets, with no response.
Guess what finally unblocked our account after 4 days of silence? We called their enterprise sales number, and it was fixed within minutes.
This is the third time we've been held hostage for multiple days with no recourse, no review, no "hey, we noticed this link, can you check on this before we block the account", or "hey, we quarantined this one email for your review while we let the other 60,000 go through, is this legit?" It goes from "everything's fine" to "we're screwed" in a heartbeat. And then we have to pay them $1000/month still! No way.