O2Popper is a mail proxy application that enables continuous use of mail software and systems that do not support Gmail's OAuth2. There are also erroneous transmission prevention functions.




  1. Supports both POP and SMTP
    • Two protocols, POP and SMTP, can be made compatible with OAuth2.
      (Supported also IMAP from version 3.0.0.)
  2. Monitoring function
    • A GUI that can monitor the communication protocol is implemented.
  3. SMTP block functions
    • You can block the mass mailing by mistaken Cc and Bcc.
    • You can cancel the transmission for up to 30 seconds.
    • You can remove the X-Mailer or User-Agent headers and send.
  4. System tray menu
    • The operation menu is iconized in the system tray and does not interfere with other application operations.
  5. Compatible with both Windows and macOS
    • Windows version and macOS version are available.
  6. Open Source
    • The source code is on GitHub as an MIT license.
    • I do not collect personal information of users.

Confirmed operation email clients

*1 This is information from the user. The author has not confirmed the operation.


Source Code

(not include secret file for OAuth2)