NOTE: Google Support note on this topic: https://support.google.com/a/answer/105694?hl=en
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  1. Sign into the Google Admin console.
  2. From the dashboard, go to Apps > Google Apps > Gmail > Advanced settings.
  3. In the Organizations section, select the organizational unit for which you want to configure settings.
  4. Under POP and IMAP Access, select or clear the checkbox for Disable POP and IMAP access for all users in the domain:Admin_console_and_2__sshIf you select the checkbox, POP and IMAP are fully disabled for all users in your domain.
    • Users cannot access POP and IMAP settings in the Gmail interface.
    • Users cannot access their mail via POP or IMAP even if they originally had it on.
    • Users cannot access or search mail via Google Desktop (which uses POP).

    If you clear the checkbox, POP is enabled for your users, but IMAP remains disabled.

    • POP access is automatically turned on for your users.
    • Users need to enable IMAP in the Gmail settings under Forwarding and POP/IMAP.
It may take 15-30 minutes for IMAP and POP changes to take effect. As long as the box is cleared, users can configure POP and IMAP access for a host of clients.