+1 for avoiding SendGrid. We haven't had this problem at work. But we have persistently hit a bug where if you send them two API requests at the same time they

+1 for avoiding SendGrid. We haven't had this problem at work. But we have persistently hit a bug where if you send them two API requests at the same time they will return a spurious 403 error for one of them. They seem unwilling to fix it (reports go back years). We currently have a retry with random timeout configured in our system to compensate for it. I've previously had good experiences with SparkPost.