I (male) have a very good (female) friend over in the south-western United States that I met one year ago and we're exchanging mails or messages from time to time. We're both not older than 22 and I consider her a very open person. Note that this is not about dating her—just casually writing mails.
What would you suggest to end the mails with? It shouldn't sound too stiff, but also not too intimate. I definitely don't want to send "Kind regards", but also no "kisses".
In addition, I'd like to know if "cheers" is possible with US-American people?