No, leading spaces in message headers are not allowed by the spec. Nor are multiple From headers.
Multiple addresses in a single from header is technically allowed, but Google has enforced against it since implementing DMARC nearly a decade ago. A space in front of a header indicates a header continuation, which means they are interpreting the next line as a continuation of the From header, and I guess it happens to parse as another address or two. And they don't use regular expressions to implement message parsing. At least when I looked, the email address parsing code was a bit more lenient than the rfc, to try and cover emails that were obviously not generated using rfc compliant software, but should be fairly accurate. We also had a strict parser to be used in some cases, I don't recall if it's used for this or not. Brandon On Mon, Sep 18, 2023 at 7:56 AM Scott Mutter via mailop <mailop@mailop.org> wrote: > We're seeing an increase of errors from Google's mail servers complaining > about multiple addresses in the From header. But these messages do not > have multiple addresses in the From headers or multiple From headers. > > Best I can tell, this seems to be caused by additional spaces in some of > the headers, I suppose the header immediately following the From header. > > I'm not really sure who is at fault here. Are leading spaces in mail > headers allowed? > > Headers formatted as: > > From: Name <em...@domain.tld> > MIME-Version: 1.0 > > Generates this multiple addresses in From header error. > > Headers formatted as: > > From: Name <em...@domain.tld> > MIME-Version: 1.0 > > Does not generate this error and messages are sent through. > > (In case the formatting of this message does not portray the issue > correctly, there is a single space before MIME-Version: 1.0 in the message > that generates this error) > > I'm not sure if a leading space in a message header is proper. But I > would also kind of lean towards this being a wrong regex being used by > Google's mail servers to detect multiple addresses in the From header. > > Anybody else seeing this or have any insights? > > _______________________________________________ > mailop mailing list > mailop@mailop.org > https://list.mailop.org/listinfo/mailop >
_______________________________________________ mailop mailing list mailop@mailop.org https://list.mailop.org/listinfo/mailop
