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I noticed that Gmail messages have both a DKIM-Signature header and a DomainKey-Signature header, while Hotmail messages have none.

  1. What is the purpose of using both DKIM and DomainKey signatures, as Gmail does?
  2. Is it fairly safe/compliant to use only DKIM, and not DomainKeys?
  3. How come Hotmail doesn't use any of these methods?

I'm sorry for combining a few questions under one: they don't seem to warrant individual entries.

Thanks!

ezequiel-garzon
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    Googling those terms will quickly bring up the Wikipedia entries for [DKIM](http://en.wikipedia.org/wiki/DomainKeys_Identified_Mail) and [DomainKeys](http://en.wikipedia.org/wiki/DomainKeys) – Chris S Jan 20 '11 at 13:47

2 Answers2

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  1. For additional authenticity verification.
  2. If you're going to take the time to set one up, why not do both?
  3. Ask them.
gWaldo
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    DKIM "replaced" DomainKeys, almost nobody still uses DomainKeys. Very few places use DKIM either. [SPF](http://en.wikipedia.org/wiki/Sender_Policy_Framework) is much more popular and doesn't have all the problems DKIM does. – Chris S Jan 20 '11 at 13:49
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    @Chris S, Care to elaborate on the problems DKIM has? – HTTP500 Feb 10 '11 at 02:58
  • I too am interested in hearing about DKIM's problems. I've run it without issue for years now. SPF is complementary to, rather than a replacement for, DKIM. You should be using both. – blueben Feb 10 '11 at 04:14
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Microsoft is backing Sender ID - http://mail.live.com/mail/policies.aspx

Mark Henderson
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becomingwisest
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