Using the LegacyFlo application, you can migrate email data from accounts hosted on one IMAP server to another. For example, to migrate email data from a Yahoo mailbox to GSuite, you can use LegacyFlo.
You can also upload historical email data in files such as PST/EML/MBOX into Vaultastic or SkyConnect mailboxes.
For an overview of the process of uploading historical email data to Vaultastic or SkyConnect, refer to www.vaultastic.com/migration.