The test email works great but before I get the message "A test email was succesfully sent..." I get the error message: Auth login : Received wrong SMTP code: 502 5.5.2 Error: Command not recognized.
It is a standard ISP so with regular SMTP traffic.
SMTP code 502 stands for "Command not implemented", so the SMTP server is not supporting something that Gateway IP Monitor is sending. If you can tell us more about your SMTP settings (SSL? Authentication?) and the version of GWIPMON then we should be able to help.
It sounds like you configured authentication, when the SMTP server doesn't actually require that.