Comment by chias

When I joined fastmail I imported my gmail and also configured it to be able to fully use my gmail account via IMAP so I wouldn't need to sign into gmail at all.

I was also moving from a gmail address, so next I created a label that got attached to any email received to the old email address via that IMAP connection, which gave me a nice self-maintaining todo list for services that had not yet been updated to use a new email address.

I was also surprised by how flawlessly seamless the whole process was. It was a big factor in my selection of Fastmail over other competitors when I was making the decision to leave Gmail.