Quite a nice name. Not a blockbuster, but real nice.
Go email gets 320 exact monthly searches, so it's not a strong search-based domain; rather it's a strong brandable domain.
GoMail is shorter and tighter of course. But GoEmail is pretty usable too.
goemail is regged in the top extensions; and go-email regged in com/net/info. Right away this tells you there is desire for the name, so you know it's considerably more than reg fee value.
I'd appraise in the $200 - 600 range for resellers; $1500++ for end users. Mid or high x,xxx if they absolutely love it... but I think that when you enter into the higher prices, they'd much rather pay high for gomail than goemail, so your price ceiling is limited.
*All this is assuming there are no hassles from Google, since both gomail and goemail might be considered to be 'confusingly similar' or typos of gmail. Never know
Good luck. I do like the name