As you know, I've been having some issues with my mail server hanging after going to 6.5.4. After loading iSeries PTFs and finally getting some debug logs sent to Lotus (it's been about 2 months dealing with this on about a weekly basis), they told me Friday:
"I used several of my resources at IBM to conclude that this appears to be a network problem."
So, I have a communications trace going right now and am collecting random NETSTAT *CNN logs. They also think I should break out a sniffer.
Will keep you updated...