We've had a similar experience. We use them for both marketing mass emails and for ingesting support ticket emails (I believe that's through Mandrill). Someone sent a marketing email they didn't like (they said another one of their customers complained about it, or something; literally one complaint) and so they silently shut off our incoming email. We noticed it when one of our customers called to ask why we hadn't replied to one of their support tickets. They didn't bother to tell us.
It's a big bag of "do not recommend".
(As for how we manage to use them for incoming email; emails go to a gsuite inbox, which forwards them to MC/Mandrill, when then calls a webhook to actually process the email further. Yes, we could do way better with our own SMTP server that cuts them out. I think this architecture was chosen to have a failsafe in the event that our services all go down.)
It's a big bag of "do not recommend".
(As for how we manage to use them for incoming email; emails go to a gsuite inbox, which forwards them to MC/Mandrill, when then calls a webhook to actually process the email further. Yes, we could do way better with our own SMTP server that cuts them out. I think this architecture was chosen to have a failsafe in the event that our services all go down.)