Am 2012-11-15 15:30, schrieb Ralf Hildebrandt:
Today a user reported that he received a mail without attachment.

Turns out that there *IS* an attachment, but it's strangely named.

Looking at the raw mail we find:

MIME-Version: 1.0
Content-Type: multipart/mixed;
        boundary="=_v1cFiJlk+hCgpTYQg6SrNjzrUErl8abdUWfJ88KLUInW8C9C"

...
--=_v1cFiJlk+hCgpTYQg6SrNjzrUErl8abdUWfJ88KLUInW8C9C
Content-Type: application/pdf; name*0*=


"iso-8859-1"%41%6E%66%6F%72%64%65%72%75%6E%67%65%6E%5F%53%7A%31%5F%53";
        name*1*="%7A%32%2E%70%64%66"
Content-Transfer-Encoding: base64
Content-Disposition: attachment;

        
filename*0*="iso-8859-1"%41%6E%66%6F%72%64%65%72%75%6E%67%65%6E%5F%53%7A%31";
        filename*1*="%5F%53%7A%32%2E%70%64%66"


JVBERi0xLjQKJeLjz9MKMyAwIG9iago8PAovUHJvZHVjZXIgKFBERi1YQ2hhbmdlIDMuNjAu
...

If we interpret the numbers as HTML entitities, we get:
Anforderungen_Sz1_Sz2.pdf
which looks fairly normal.

Is this encoding ok? I know it's OK to encode special characters like
Umlaut characters. But all of it?

Also I have never seen this "line continuation" of the filename/name
field. Is that legit?

I've never seen this stuff before...

Ralf,

it is correct. You find the explanation in

RFC 2231
MIME Parameter Value and Encoded Word Extensions:
Character Sets, Languages, and Continuations

Gruß,
Michael

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