I like DuckDuckMail, because it follows DuckDuckGo, and DuckDuckBot, but it is a little too long. Maybe we could abbreviate it to DDM, or something else.
duckmail.com and duckit.com domains are already registered. Seems to me that they're already out of the game since I don't think DDG would want to spend some thousands of dollars just to get one of those domains.
duckduckmail.com is still available and dukgo.com is already registered by DDG.
Do we have to choose only one? We could be offered a drop-down list with "@dukgo.com" and "@duckduckmail.com" at sign-up time.
Hotmail has many domains to choose from (e.g. hotmail.com live.com live.etc) even Gmail has gmail.com and googlemail.com (they had to setup the latter for for legal reasons if I understand correctly)