Just for the record, Mailtrain is used in production by several marketers with very large lists (from hundred thousand subscribers to a million subscribers) and Mailtrain seems to work fine for them
Is there anything to read that's public where those marketers comment about using it?
Have any of them done any audits on the code base and traced all incoming requests through Mailtrain vs their SES backend to ensure everything was delivered as expected?
Have any of them done any audits on the code base and traced all incoming requests through Mailtrain vs their SES backend to ensure everything was delivered as expected?