MailChannels is the service other services use, it's the de facto leader in combating spam. They are mostly meant to be used by high-volume hosted email service

MailChannels is the service other services use, it's the de facto leader in combating spam. They are mostly meant to be used by high-volume hosted email services. They are very good at detecting abuse. The leading cause of email deliverability problems is not advertisement, it's servers being hijacked by malicious actors.