I could pay more to have a dedicated IP at sendgrid, but that's a lot more expensive. I could also move to another service (SES, Mandrill, ...) but I'd like to ask opinions if that would be any better, since I would also be on a shared IP pool over there. Anybody that can share their experiences in this regard with these other services?
Edit: Apparently there is a free tier (100 emails per month). We went for the $10 for testing, it's cheap.
I'd also be curious to hear how I can make my system more robust in the face of these issues. Right now, Sendgrid reports these emails as "successfully processed" and so I don't have a good way to programmatically retry these jobs.