--On 29 January 2008 15:56:44 +0000 Mike Cardwell <[EMAIL PROTECTED]> wrote:
>> 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. I didn't say that you can't use it. I said it's non-standard. However, although I'm unable to find the rfc that suggests it, it's quite common to use X-something for non standard headers. It's certainly unwise to use something that might later be registered for a different purpose. > >> 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 can't. However, we all use lots of spam detecting heuristics that aren't justified by RFCs. >> 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 -- Ian Eiloart IT Services, University of Sussex x3148 -- ## List details at http://lists.exim.org/mailman/listinfo/exim-users ## Exim details at http://www.exim.org/ ## Please use the Wiki with this list - http://wiki.exim.org/
