As I read it, it was changed to limit the damage Trojans or worms could cause where they use their own SMTP engine - or am I talking uninformed gibberish?

So far I certainly recommend the waitdelay change!

I suspect your TCP/IP stack is corrupt

Google for "(fix OR repair) TCP/IP stack"

edited to add:

This - http://www.snapfiles.com/get/xptcpiprepair.html - utility is reputed to be OK [never needed to try it, so can't vouch for efficacy]

Saw the word 'corrupt' and practically had a heart attack:D .

Had my early morning 'Google' thanks, but I have no 'symptoms' of such AFAIK, so I THINK all is now well with the modified wait_delay. Certainly the ADSL connection disconnects immediately and the beast shuts down cleanly every time.