There have been some really good observations and suggestions in this discussion. Thanks to all who've contributed. If I may make another observation.
If you haven't already noticed from some of my other posts, I have a pretty dry sense of humor. With people who know me well, I often use sarcasm. But with people who don't know me well, I've found that using sarcasm often results in being taken literally at first, especially in written form when the recipient can't see my facial expression.
I've found that when writing to people who don't know me well, to avoid misunderstandings, it's better to either avoid sarcasm or make it really clear that I'm trying to be humorous. 
