If someone hasn't replied to your PM, you can check to see if they've even read it by checking to see if it's in your Outbox.

Messages are stored here until they are read by the recipient, after which they are moved into the Sent Box.

This is actually quite handy as it means you can edit the messages still before the person reads it.

However, if the person hasn't read the message yet you can generally assume they are away or too busy to deal with it

- but not necessarily ignoring you

(of course, they could just not be reading any PMs from a specific person, but you'd probably see them posting elsewhere and get a bit suspicious.

.

.

).

I can see the merit of out of office function, but at least there is an alternative if they are never implimented as a feature.

HTH.
