[ietf-822] Mail headers on crack....

[[e-mail]]

(Not sure if this list is still active, trying anyhow...)

So I'm updating my "List of things that the exmh MUA gets wrong", and I
have this in an item in the folder I use as a rogue's gallery of test cases...

MIME-Version: =?UTF-8?B?MS4w?=
Content-Transfer-Encoding: =?UTF-8?B?OGJpdA==?=
Content-Type: =?UTF-8?B?dGV4dC9wbGFpbjsgY2hhcnNldD1VVEYtOA==?=
Content-Disposition: =?UTF-8?B?aW5saW5l?=

Ugly as it is, I can't find where in the RFCs it says this is a no-no. Or
is this actually wonky-but-legal?

(I have to fix it in exmh whether this case is legal or not - its decoder
for UTF-8 in headers in general gets the length wrong and occasionally sticks 2
extra corrupt bytes onto the end of the decoded string)