Although this doesn't answer the question directly, as there isn't a 'standard sign-off email' at least that I know of, the underlying problem is more important.
As far as I am concerned 'shipping' is a business decision. Not a decision made by the tester/QA or the team. I wholeheartedly concur with this when testers are asked for ship/noship opinion and have a read here.
Your job is to inform. As has been mentioned elsewhere: communicate what you have done, how you did it and what you didn't do. So others can make informed decisions based on what you provided and on information provided by others and information you don't even know exists.
To me it seems as you are being setup to be the scape goat, the fall-guy or at best the 'one to make the decision so no-one else has to'. That is not your role, and I assume you are also not being paid for it.
Originally added as a comment, I added this as an answer on a nudge from @32hedge ;-)