Really, they're a metaphor for relationships in general. I mean, if you want to maintain your friendships you have to work at them. You think of the other person to see how you can meet their needs, right. That's what being a friend is. To me, as a guy, that's the "loving" part. You wade through the putting up with little idiosyncracies, the annoyances, and even bad attitudes to get to the nuggets meaning something to somebody and them meaning something to you.
It doesn't matter what form of relationship you have; family, friend, lover, they all require this same effort. Why do we find it so difficult to do with our siblings, our parents, and our lovers what comes so easily with a casual friend. Could it be, 'we've allowed anger or fear of hurt, a get back at you spirit to steal the special joy readily availabe in every relationship. That's where the work comes in. You have to set aside those emotions or work through them to maintain the special connection friends easily enjoy. The reason friends find it so easy is because of the lack of commitment. If they hurt you or keep you angry, its easy to dump them and find a new friend. Each party is aware of the lack of commitment and so use more caution in relating to the other.
The chain mail is an example of this. Its not harmful or hurtful, just a misguided attempt to share a blessing. Their hearts are right, the message is loosely, "I thought of you when I saw this. Just a reminder that you are still in my heart." This is their way of working at it. I recognize that without these chain letters, in many cases my friendships with the senders would be shelved because of the literal distance between us. With all of our moving around the country there are many hundreds of miles between us. So what can you do to keep a friendship from drying up due to the winds of time and distance.
I make a lot of phone calls. I use the heck out of the free nights and weekends on my cell phone service. I'm terrible about sending cards and that sort of thing. I use the instant messenger if I can catch anybody online. The easiest thing, I guess is to forward a chain letter because they're interesting or touching, or at least informative, you know what, I love chain letters.