Here is archival documentation of the U.W. Dept. of Chemistry’s project of outsourcing email service from 2014 to 2015.
A phased implementation allowed us to outsource SMTP, IMAP and POP3 services without interruption of service.
To facilitate the migration of approximately 100 email accounts, I prepared the following email user migration guide to migrations and migration web app (the web app pages are de-actived).
The more tech-savy users were able to self-migrate using the guide and the web app.