About a year ago or so I was involved in setting up an intercorporate PVC between a client's network and one of our networks. We got together on the phone and we agreed on an addressing strategy which would work for both companies. I asked him to please confirm the address space in e-mail and we would get going on the project.
I never got the confirmation and on the next conference call he said that he had sent it. I looked again, and nothing. He resent, again nothing. I then asked him to send to my home e-mail address and BINGO, it appeared within a few seconds.
One sentence in his mail was to this effect:
'As we discussed, we will use the address space 192.168.42.xxx for the LAN at your facility.'
Yes, you guessed it, our mail filters caught the 'xxx' and thought it was something nasty and dropped it.
It was somewhat embarrassing on our part.
Good day JSW