I noticed that Gmail messages have both a DKIM-Signature header and a DomainKey-Signature header, while Hotmail messages have none.
- What is the purpose of using both DKIM and DomainKey signatures, as Gmail does?
- Is it fairly safe/compliant to use only DKIM, and not DomainKeys?
- 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.