Just now I have setup POLYCOM Viewstation H323 behind a PIX and in a "DMZ" under the FWSM ... it seems the Calling has started at the foreign POLYCOM, but the call cannot complete connecting. I have noted at the foreign POLYCOM that has picked up a Calling partner of the internal (before NAT) address, which i wonder if that causes the problem !! but WHY ? ... note : my Netscreens have no such problem !!!
Cisco Fixup is no good, ... have experience before about ESMTP
see this note :
Note: If you have an ESMTP server behind the PIX, you may need to turn off the Mailguard feature to allow mail to flow properly. Also, doing Telnet to port 25 may not work with the fixup protocol smtp command, especially with a Telnet client that does character mode.