Ian Eiloart wrote:
>>>> The "headers_remove = User-Agent" line is something entirely different
>>>> that tends to help. You'll find many references on the web to hotmail
>>>> blocking certain messages that contain Thunderbird in the User-Agent
>>>> header, but allowing through messages that are exactly the same, but
>>>> without the User-Agent header. I tested this myself a while back and it
>>>> was true.
>>> Why would an MUA add a "User-Agent" header? It's an HTTP or net-news
>>> header, not a mail header.
>>> <http://www.iana.org/assignments/message-headers/perm-headers.html>
>>> Arguably, Microsoft are doing the right thing by punishing clients for
>>> using non-standard headers.
>> Non-standard headers? You can add *any* arbitrarily named header you
>> want to an email. At least Thunderbird and Mutt both use "User-Agent".
>> I've not tested other MUAs. Microsoft aren't, "doing the right thing,"
>> or anything even close to sensible by scoring so harshly on this header.
>
> RFC2822 does say that you can add other headers, but not arbitrarily named
> - the name can't clash with a registered name.
I can't find where it says that... It does list a bunch of headers that
are to be used to store a certain type of information such as "Subject,
From, To" etc, and I can see why you wouldn't use those headers for
storing arbitrary data. Eg: "From: Thunderbird Client" would be bad.
But I don't see anywhere where it says I can't use "User-Agent: Whatever
I want" in email headers.
> However, that doesn't mean
> that every imaginable header is "Standard". Indeed rfc2076 lists several
> headers as "not internet standard". I'd suggest that a "standard" header is
> one that's registered with IANA according to rfc3864:
> <http://tools.ietf.org/html/rfc3864>. I guess, for clarity, I should have
> used the phrase "registered".
Hmmm. Can you quote a relevant passage from a relevant RFC that says or
even mildly suggests that you "MUST NOT" or even "SHOULD NOT" use this
header for this purpose?
> I suspect that Microsoft are adding spam points to messages with
> non-standard headers, which would explain why some messages are acceptable
> when they don't contain a user-agent header.
Email systems add all sorts of unusual headers to emails. I'd suggest
that it's less likely for a spam to contain a "non-standard" header than
a ham, not the other way round.
Mike
