Header param encoding

[juhlig]

gen_smtp/src/mimemail.erl

Lines 924 to 929 in c6f25a7

	encode_parameter({X, Y}) ->
	YEnc = rfc2047_utf8_encode(Y, byte_size(X) + 3, <<"\t">>),
	case escape_tspecial(YEnc, false, <<>>) of
	{true, Special} -> [X, $=, $", Special, $"];
	false -> [X, $=, YEnc]
	end.

I think this is wrong (though most Mail clients seem to accept it): Parameters should be encoded according to RFC 2231, not RFC 2047.

[seriyps]

Oh, interesting. This change have been merged quite recently #235. But I think it would worth to add support for RFC-2231 (in parser as well; including multiline params)

[Maria-12648430]

#311 is about the encoding of parameter values. I'll see what I can do about decoding in a later PR (probably quite tricky, it looks like many clients do it wrong, so we need to be able to parse both RFC2231 and RFC2047), but I think first this PR should be carefully reviewed.

[Maria-12648430]

I noticed some bugs in header parameter parsing that I need to iron out before tackling the actual decoding 😞