GMail: IMAP security (OAuth2)
As of v4.2, POP Peeper supports OAuth2 for GMail IMAP/SMTP (it is not currently supported for POP3).
To use OAuth2: edit your GMail account in POP Peeper and change the 'password' dropdown to 'Oauth2' (next to your login name). For versions prior to v5.2, press the 'Oauth2' button.
There are 2 options available: either setup 2-step verification and create an app-password for POP Peeper or enable access for "less secure apps":
1) Enable 2-step verification
2) Create app-specific password Allow less secure apps
This option is much easier to setup, but provides less security than 2-step verification (note: it does not make your account unsecure)
1) Allow less secure apps