It's long been the case that esps emit the most junk, not marketing but actual spam: stolen credentials, many many vulnerabilities, trials etc
These days sendgrid is the highest followed by Google and mailgun, Microsoft used to be on top but they seem to have dealt with it a little (anecdotal logging for mail servers I manage)
In fact Postmark only supported transactional email (and had an approval process) in the past. It looks like they dropped that to pursue a larger market, with predictable consequences.
These days sendgrid is the highest followed by Google and mailgun, Microsoft used to be on top but they seem to have dealt with it a little (anecdotal logging for mail servers I manage)