Update!
The case of my own BB 9700, using the o2IRL network, and its failure to read the 'Reply-to' field has been solved, that is, the cause has been established.
Some detail here:
http://community.o2online.ie/t5/Blackberry/Failure-of-BlackBerry-Internet-Service-to-read-REPLY-TO-f....
The error lies in BIS. It incorrectlys read MSNMSP (Microsoft's Mobile Services Protocol). If however, you force BIS to read the POP3 protocol for Windows Live, the error - apparently - disappears. I say 'apparently' as I have not tried it, and won't. Using POP3 seriously degrades other functions.
The next upgrade of BIS may, I am told by RIM via o2IRL, fix this.
A similar answer to this may well apply to the same problem, but with different networks and different email providers, identified by other users in this thread.
It is also clear that the BIS configuration varies between networks. For example, Verizon in the US uses (or has been using), for Windows Live addresses, POP3 by default. The dafault though for BIS as used by o2IRL (the o2 network in Ireland) is MSNMSP.
MSNMSP is what Windows Live offer mobile client services, such as BIS/RIM. A different protocol is used for their own mobile site for email, wherein the 'Reply-to' header is read correctly.
Frankly, this is a dog's dinner!! A client service which does not read the 'Reply-to' field correctly should not be offered to the public. It's like selling a car with no reverse gear. Let's hope RIM do in fact deal with this.
