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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.


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Googling those terms will quickly bring up the Wikipedia entries for DKIM and DomainKeys – Chris S Jan 20 '11 at 13:47
  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.
share|improve this answer
DKIM "replaced" DomainKeys, almost nobody still uses DomainKeys. Very few places use DKIM either. SPF is much more popular and doesn't have all the problems DKIM does. – Chris S Jan 20 '11 at 13:49
@Chris S, Care to elaborate on the problems DKIM has? – HTTP500 Feb 10 '11 at 2:58
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 4:14

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