If captcha is enabled on your GMail account (and it is enabled by default), then GMail POP3 authentication will fail with this error (even though a correct login/password is provided)

**** Connected to pop.gmail.com:995
< +OK Gpop ready for requests from c23pf1097242ibu.22
> USER myaccount@something.com
< +OK send PASS
> PASS ****
< -ERR [AUTH] Username and password not accepted.

To successfully authenticate with pop.gmail.com from an email client such as Outlook, Thunderbird, or an application using Chilkat one must first unlock captcha:

  1. From the computer on which your signins are failing, visit http://www.google.com/accounts/DisplayUnlockCaptcha
  2. Enter your Gmail username and password, and the letters in the distorted picture.
  3. Once you have successfully signed in, retry running your application using Chilkat.

Note: Unlocking captcha is not required to access a GMail account via the IMAP protocol (imap.gmail.com).