I just wanted to tell to everybody who followed that I sucessfully fixed the problem - thank you for the replies!
How?
I successfully installed and configurated postfix. Bredbandbolaget (the ISP) is set in a way that outgoing mails jsut can be sent out over the server smrp.bredband.net - since this server also demads a sasl authentication it was necessary to use my friend´s log-in name and pw.
I´ve got the informations herefor out of the read me file that comes with postfix
The only restriction is that some spam filters of email providers will filter these mails as spam because the server that is being used to send out the email does not match with the email provider that is used in the sender address (not bredband but still my normal sender address which is a gmx-address)
If this applies depends on the spam dilter settings of the recipient.
But then it is still posssible to send out a webmail-based email in order to inform the people for whom it really matters that they have to receive your email. Then they can change their filter settings.
I hope that these informations can be helpful for anyone in a similar situation in the future.
cheers,
walking
