A quick Google search suggests this may be a POP configuration issue in your Courier setup.
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puzzling dot org: Courier IMAP/POP SSL errors
When I do 'openssl s_client -connect myhostname:995', I get: CONNECTED(00000003) write:errno=104
You need to change your TLS_PROTOCOL configuration file variable, and possibly (if you have it) your SSL_PROTOCOL variable to allow SSL version 2.
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You might want to compare your IMAP and POP config settings.
Maybe POP SSL is not configured right.
/etc/courier/courier-imap-ssl
/etc/courier/courier-pop-ssl
-Rick