I just send out the invites, I don't pm anyone, because I have had loads of invites from airlines over the years I've played this game and if I don't want to accept the invite I reject it, it's called common decency in my opinion and it's only takes a second of your time.
Oh and I have pm'd the recipient after a couple of months (game time) asking them if they aren't going to accept, please could they reject the invite. I have to say I have got, around 1 in 10 replied to my request. I call that ignorance, which is so rude, I'm sorry to say.
Yes I know the invite expires after a year (game time) I reckon that should be reduced to 6 months (game time) for the people that are too ignorant to reply.
Just my opinion and I'm sorry for any upset that my opinion causes.