From the source of OTRS I would suggest that it's not an authentication issue, but that it fails to establish an SSL connection. The reason might probably be, that you use a kind of recent IO::Socket::SSL version, which has certificate verification enabled by default. This version of IO::Socket::SSL already uses the default CA store location of OpenSSL, but on windows this might not work (openssl assumes either a file in PEM format or a hashed directory).
The bundled version of Mail::POP3Client is not aware of any certificate verification, e.g. it does neither provide useful certificates nor does it switch verification off. This is fixed in the current version of OTRS, where they don't use Mail::POP3Client any longer but instead the core module NET::POP3 enhanced through Net::SSLGlue::POP3 - and here they switch certificate verification simple off (which means, that man-in-the-middle attacks are easy).
What you could do:
the best way would be to get the necesary CA certificates and put them into a file, then let IO::Socket::SSL use this file. You might use Mozilla::CA for this (like LWP does) and then somewhere in your code (as early as possible) load IO::Socket::SSL and set the default verification path:
IO::Socket::SSL::set_client_defaults( SSL_ca_file => Mozilla::CA::SSL_ca_file )
or switch verification off, like done in recent OTRS versions (and close your eyes to not see the obvious security problems), e.g. IO::Socket::SSL::set_client_defaults( SSL_verify_mode => 0 )
- or upgrade to recent OTRS version which "fixes" the problem by disabling certificate verification