wearedementors our IMAP storage servers are massive bare metal machines.
heymrdj Be interested in your thoughts on backup and Pop v Imap
If he uses POP3 then he'll have access to his mail only on a single device, unless he's doing POP3 downloads on every device. Even then, his mail will be in different states on every device, sent messages would only be stored on one device etc.
Also if their POP3 settings are to delete messages after downloading then he would lose the ability to read his old mail on the webmail server.
It also means that when he gets a new computer or device then he'll have to transfer the mail to the new device manually. If the old device is dead and they've got no backup, then their mail is gone forever.
If none of that is important to your client then POP3 would be OK I guess.
My choice for my own stuff is always IMAP + personal backups.