I think a PlusNet member`s email address is sending spam.... what should I do?

[#1]

It`s all in the title....
what should I do?
What Can I do.?
who should I report it to?

[#2]

Report it to PlusNet

[#3]

I tried reporting a similar problem to Plusnet a couple of years ago, and I got a reply along the lines of - it's not Plusnets responsibility to alert other customers regarding potential security issues with their machines.
In the end I just blocked the half dozen or so problematic Plusnet users from my network, and it was no longer MY problem.

[#4]

Theoretically you should report it to abuse@plus.net - but I've seen posts in the past that this doesn't achieve much.
Perhaps setting up a rule to forward them to j.ford <at> plus.net might get the problem noticed!

[#5]

Do the headers identify the original source IP address as being in a Plusnet controlled range? If so then you can try dropping a note to abuse@plus.net including all the headers so they can try to do something about it.
If the originating IP address isn't a Plusnet one then you can try and send an email to the relevant abuse address for that network, although this'll probably have no use whatsoever.
Note that using the From: address to determine the source of spam is next to useless - it's a trivial exercise for a spammer to create emails with a From: address of anything they want 
Alternatively just mark the email as spam and move on....

[#6]

Thanks for the input, guys.... I will send the header to abuse@plusnet..... It is not a "malicious" report, more a "security issue" for the person who`s email address is being used.... My sister had a BIG problem with similar a couple of months ago... and that was a BT email address...