I am unable to migrate one mailbox to office365 which is used for sending bulk email during add campaign time for clients. Office365 a mailbox from sending more than 2000 email in an hour. However, I am thinking about creating five numbered suffix mailboxes beginning with same mailbox and distributing campaign emails by sending 1800 per mailbox.
My current on prem campaign mailbox has following characteristics -
Every campaign email that goes out has a duplicate that also goes to email@example.com (for liability).
It varies, but generally about 8,000 emails per hour get sent to firstname.lastname@example.org during a campaign run. Last run on moth/year was about 47,000 emails (ran from 5:27pm to 1:05am).
We're using Postfix on linux server to route mail from SQL server to skpost (for recipient send out) and locally to exchange (the duplicate explained earlier). It's possible to throttle the send rate , but we also need the send out to finish before business hours the next day.
Sending bulk messages via O365 is a bad idea and can get the mailbox or sending IP blocked. Use a third-party service that specializes in bulk sending instead, every major player in the field is recognized by O365 and should have no trouble delivering (legitimate) bulk messages.