When a new instance of wxPOP3 is created a SendLine of "QUIT" is sent, but since no connection exists yet, the wxSocket code throws an assertion of an invalid socket :
./src/common/socket.cpp(1136): assert "m_impl" failed in DoWrite(): socket must be valid
A quick workaround is to wrap the code in wxCmdlineProtocol::SendLine() with an IsConnected() check.
wxWidgets 2.9.1
OS X static libs
It does not seem to be present anymore in the new version of wxEMail.
Could you confirm you still encounter the bug with wxEMail-1.0-Beta-2 ?