This actually wound up being very easy, primarily because my existing email uses IMAP – it turns out that G Suite’s Migration tool – a part of the Google Admin console – is able to import e-mail from any of the following sources:
- GMail or G Suite
- MS Exchange 2003 or later
All I had to do was to follow these instructions. The migration itself can take a long time, depending on the size of your e-mail collection.
One thing to keep in mind: if the e-mail service provided by your ISP is POP3, it may be worth your effort to get in touch with them and inquire about getting moved to an IMAP service just for the sake of being able to accomplish this migration.