can't really help you with fixing other webmail systems, but you'll probably want to verify that the url, after redirect, is in fact the correct url. other than that, the best thing I could think of is safely handling the exception and make sure the email notes about copying and pasting the url.
Thank you for your reply!
I was able to examine the error: The problem was, that instantiated the List class to early. So I got no results for this id. Now it works correctly. What I don't know at all is, why it worked correctly when I copied and pasted the url. But now I am happy that it's working.