Not the OP, but my personal experience has been that it was a mistake to rely on SendGrid. This is based on a 2016 incident [1] where SendGrid made unannounced changes to IP pools, resulting in sent emails being delayed for several hours or more while the new IPs warmed up. For many kinds of transactional email, several hours' delayed delivery quickly turns into multiple end users opening support cases. ("Where's my password reset?")

If this had been a simple mistake, fine (all ESPs have occasional issues), but to my knowledge SendGrid has never acknowledged this as an operational error. In fact, at the time SendGrid representatives repeatedly insisted the change was made intentionally for its (paying) customers' benefit.

(That said, SendGrid had some really nice tracking and segmentation dashboards, which I do miss at my new ESP.)

[1]: https://news.ycombinator.com/item?id=12142728

I meant Mandrill—Mandrill was a significant mistake. SendGrid is working great for us. So sorry.