As a former Sendgrid Customer, the big thing that no one has commented on is that Sendgrid's internal "Reputation Score" is complete BS. We had a 98% score, and all the meanwhile our Gmail and Microsoft reputations had been tanking. It took us over a year to switch providers and rebuild a proper reputation with new IPs, and better sending patterns, unsubscribe policies, etc.

Monitor Gmail's & Microsofts actual Postmaster tools, use a tool like MXToolbox for blacklist monitoring. Sendgrid's internal scoring is completely broken, and they don't care.

Sendgrid/Twilio has given up.