So bottom line, don't bother.
You get lost in a strange city, and are looking for your hotel. You go up to some guy and ask for directions and he says, "Go three blocks and turn left. By the way, I assure you that's the way to the hotel, and it's not going to lead you into an alleyway where you will be jumped by my two brothers, one of them has a knife and one of them has a gun, and as long as you cooperate you won't get hurt. Nothing of that sort will happen. As a condition of following these directions, you agree not to tell the police about this conversation."
So, instead you get into a cab, and the cabbie says, "Oh, you want to go to the Hilton, no problem. I will take you straight there, and will not drive around to run up the meter and then hand you over to kidnappers who will force you to take all of your money out of an ATM before leaving you stranded. Nope. The Hilton here we come, just as long as you sign this form relieving me of responsibility for anything that might happen to you after I drop you off."
Be real. Be honest. Be yourself. Say why you think the name is worth what you are asking. Your defense to being blindsided by some obscure trademark claim you've never heard of is then built-in to what you've said. Always assume that whatever you send by email is going to show up as evidence somewhere. As you think about what you want to say to whomever you are addressing, also think about how it will look to someone else reading it.
If you've had the domain name since 2010, and you know there is someone running around with a trademark they acquired in 2015, then (a) first make sure the domain name isn't doing anything related to that trademark and (b) mention in your reply, "I've owned this domain name since 2010, and I believe it would be useful for (something other than the subject of the trademark)." Then, when you run across the usual statement in a c&d letter or a UDRP complaint which uses the stock phrase, "We recently became aware that you registered whatever.tld," you can point to where you TOLD them you've had it since 2010.
http://www.wipo.int/amc/en/domains/search/text.jsp?case=D2011-0005
In this case, the Panel is satisfied that the Complainant’s representatives were well aware of the importance of the chronological issue - the Respondent’s attorney had alluded to it in pre-action correspondence and indeed the Complaint specifically referred to the question of whether the disputed domain names predated the trade marks.
