Hi Robert,
thanks, I did help me at the time.
I would like to mention, though, that now after upgrading to 2.18 sub createEmailSenderTransportSMTP is no longer found in the file /opt/webwork/webwork2/lib/WeBWorK/ContentGenerator.pm, but in the file /opt/webwork/webwork2/lib/WeBWorK/Utils.pm.
Hope that helps someone else.
Bernd