Your email message is sending an important message back to you. Namely, think twice about your written words, no matter where you write them. And if they are "offhand" comments about people, you don't need to think twice. Rather, don't even think about it.
You actually do not know if the target of your offhand remarks even read your comments. Perhaps he or she never read any of it, but is giving you the big chill for other reasons. Maybe this person is cool to everyone right now.
One option is to let some time pass and see if he or she warms up. If you are deeply concerned about what may have happened here, you should talk with this person. If you do, open the conversation by saying you have noticed that he or she seems upset lately, and you would like to know if there is anything you can do.
The next step is to listen. This person's response will let you know if your next words should be words of apology, support, sympathy, or guidance. Regardless of the outcome, it is also worthwhile to think about how you can actually help struggling co-workers rather than emailing offhand comments about them.
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