There are a lot of ways to end a correspondence. "Sincerely", "Yours", "Thank you", etc. I have noted an increased usage of "Very respectfully" on emails that I receive at work. Not just "respectfully"; I guess that would appear to be not as respectful as needed. Perhaps the recipient would think, "Respectfully? How respectful? A little respectful? VERY respectful"? And don't even use "Respectfully Yours", which implicitly implies more of a relationship than you may want.
Here's the thing, though: your correspondence is not always respectful. As a matter of fact, sometimes you are downright bitchy. Here's what I suggest:
If you are going to try to make me feel stupid, use "Condescendingly".
If you are nice on the surface, but there is thinly veiled hostility, use "Passive-Aggressively".
If you respond that you are not the right person or that you simply don't know, and don't point me in another direction, use "Not helpful in the least".
If you answer my question with waaaaaay too-much-mostly-irrelevant-info, use "Trying to look smarter than I am".
If you send four messages to answer one question, use "Clogging your inbox".
If you are just all-in bitch-mode, use "Fuck you".
I think these are pretty damn solidly truthful ways to close correspondence. I'm sure there are some other great ideas out there. What are some of your suggesions?