My customers are very old-school and I have finally convinced them to switch to G-Suite, however now they want all their old emails uploaded to the new gmail account.
Assuming they were using Outlook and messages are stored as *.pst files...
- Setup IMAP access in the Gmail account and connect it to Outlook: Instructions
- In Outlook, open the old Outlook Data (pst) File: How to
- In Outlook favorites bar, both the old and new accounts inboxes, sent items will be visible. Copy / paste or drag and drop old messages in to new accounts location. Instead of doing it manually, it is also possible for Outlook to automatically import / export, but I prefer doing the first way..
- Disable IMAP access in the G-Suite / Gmail account if it is not needed.