IMAPcross-premisescoexistence.
There is a lower probability option with existing IMAP-based mail systems for implementing crosspremiscoexistence.
This approach might be necessary with thirdparty email systems where there are more than 2,000 users.
POP3 or proprietary connections.If the third-party email system only provides POP3 or a proprietary protocol over which users connect to their mailboxes, the only migration options are:
o PSTmigration if the users have Outlook.
o Third-party POP3-based migration tool if they do not use Outlook.