Richmail in onlinedev


I'm trying to test the richmail extension in the outsystems open server onlinedev.

I think I've done everything right.
I used the RichMailAuthenticate action with kind 'PLAIN', then create the email with RichMailCreate action and finaly the SendMail action.

I'm using my account from gmx free SMTP server that provides the 'PLAIN' kind.

But when testing it I get the following error:

"A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond at System.Net.Sockets.TcpClient.Connect(String hostname, Int32 port) at OutSystems.NssRichMail.SMTPMail.SendMail() "

Am I doing something wrong?
Or is the onlidev firewall, or anti-virus, preventing me from sending mails?