SendGrid is a very popular platform for programmatic email, as is the original Twilio for programmatic SMS. They have a very solid API and integrations, so are often a go-to for developers who want to offload the work of sending emails (account registration, notifications, password reset, order confirmation) and SMS (verification codes, etc).
Unfortunately Twilio (and thus SendGrid) is also used heavily for “marketing”, which in turn means they’re great for spammers too.
Still, I would never recommend IP blocking one of the largest programmatic email senders in the world. Inevitably your end users are going to miss something important, and while you may have saved them from hundreds of spam messages for every one important thing that they end up missing, we both know what they’re going to remember at the end of the day.
Edit: Realized I never answered your actual question. Here is a list of companies Twilio claims to provide email services for: https://customers.twilio.com/en-us/sendgrid
Fair enough! Maybe if enough organizations follow suit, they’ll be forced to stop ignoring their service being used by spammers and scammers.
Right now they have no incentive to stop abuse on their platform, because they’re making money off of that abuse too. It’s bullshit.