We have everything setup now and its working just fine.
One question:
I would like to add a word (salutation) before the recipient’s titel depending on the sex of the recipient (for example “Chere Madame” “Cher Monsieur”).
Is there a way to get the sex or title as a php variable?
If not, which script creates the newsletter tags? (I might do the insertion there)
You cannot use PHP since the generated email is HTML and does not contains PHP anymore. So there is not a way, you should add a new tag modifying the plugin.php core file.