IMAP doesn't sync stuff like calendar, contacts, tasks, settings, email filters (not usually, anyway), and many online clients will only download the email headers in bulk, not the contents; those are often lazy-loaded in when you open a message, especially from more than two weeks ago.
A more reliable way to transfer email would be to download all email through POP3 and then copy them over to an IMAP account on the new server.
You can definitely export your account information (in fact, European data portability laws pretty much require Google to provide such a functionality) but importing it may require some custom tooling.
Unless either Google or the receiving party provides an official migration tool, migration is probably a pretty sucky experience. I know it can be done (companies and educational institutions switch between Google and Microsoft all the time) but I'm not sure if there's any good migration path unless you can get in contact with someone from sales.
A more reliable way to transfer email would be to download all email through POP3 and then copy them over to an IMAP account on the new server.
You can definitely export your account information (in fact, European data portability laws pretty much require Google to provide such a functionality) but importing it may require some custom tooling.
Unless either Google or the receiving party provides an official migration tool, migration is probably a pretty sucky experience. I know it can be done (companies and educational institutions switch between Google and Microsoft all the time) but I'm not sure if there's any good migration path unless you can get in contact with someone from sales.