We looked for solutions, and it appeared SendGrid was the leader in the space, so we went with the leader.

We did look into SendinBlue. 

Yes. MailChimp and others. But they were more designated for marketing emails. The majority of the emails that we send are for internal and external notifications only. And SendGrid satisfies the two worlds.

We tried own SMTP on AWS, which caused our mail to be blacklisted.