It used to be possible, when looking at another trader's profile, to see whether they had unread messages on their trades.

It was useful to be able to see whether the other trade had read the messages you sent them.

That feature has apparently been removed (I tried this out by sending a message to a trader and then viewing their profile). Unfortunately, there's no upside to this removal, and considerable downside. I don't want to spam another trade with messages, but if I can't see whether they've read what I've previously sent, I can't tell whether further messages will add to the queue. On the other hand, if I can see that they have in fact read my messages, it's more likely that they simply forgot to respond.