Moving and migrating email to GMail

I needed to help a family member move their email from a very space limited email account into a nice roomy comfortable GMail account.

No problem I thought, Thunderbird will do the job. Load both accounts as IMAP folders, and drag and drop.

Well, no.

The email moves thats true, but Thunderbird does not save the dates of the emails. All the email shows up as brand new.

Not good!

Fortunately being a Mac user I was able to use Apple Mail to move the emails over.