If you use NoSpamProxy Large Files behind Microsoft TMG, you will get error messages if you send files containing umlauts via NoSpamProxy. The error message is very cryptic and only indicates that it is an internal server error. A 500 type error message is displayed. The reason for this message is the use of so-called high bit characters, which are forbidden by default in Microsoft TMG as part of the HTTP security filter.
If you activate logging in TMG, you will see that a connection has been denied:
To solve the problem, the high bit character must be allowed in the HTTP policy in the rule.