On Friday 15 January 2010 09:29:37 Mark Martinec wrote: > On Friday January 15 2010 09:11:27 Kārlis Repsons wrote: > > But have you seriously seen a mail client, which would allow sending such > > mail? I would think, this is an extreme rarity, but is it? > > It is very rare alright. > > Multiple author addresses in a single From header field are legitimate, > but some mail processing software breaks on them. > > Multiple From header fields are prohibited by rfc, but that does not > stop malicious or broken senders from doing it if they feel like it. > > If one or the other turns out to be profitable for malware, > it will be used, no doubt about it, so better be ready. > > Btw, of the header fields that may occur only once, it is currently > more usual to see multiple Message-ID, or Subject, or To or Cc, > or MIME-Version, or Content-Type. Very rare are duplicate Reply-To > or Date. The least common is to see multiple From. > > Mark Thanks!
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