That sucks. Like you said already, especially the communication and handling of the situation. Although it is really hard for email services to keep spam outside and their services healthy (stay off spam/deny lists).
Currently I am trying out Sendgrid, which is now owned by Twilio. For the other Twilio services they are always clear in communication with great guides for everything. This seems to be the case for Sendgrid as well (so far):
https://www.twilio.com/sendgrid/email-api
(little plus, they have Azure Functions integrations)
MailChimp has been working for me pretty well in the past. They have transactional emails too, this used to be a separate service called Mandrill: https://mailchimp.com/features/transactional-email/
Currently I am trying out Sendgrid, which is now owned by Twilio. For the other Twilio services they are always clear in communication with great guides for everything. This seems to be the case for Sendgrid as well (so far): https://www.twilio.com/sendgrid/email-api (little plus, they have Azure Functions integrations)