Sudden influx of bounced messages

[#1]

Between 12:38 and now, I've had 36 undeliverable mails sent back to my xxx.plus.com address (which I *never* use since I have my own domain hosted outside of PlusNet).
Am I the only lucky recipient of these messages (which Magic Mail is currently holding for me) or is there a new round of junkmails being sent out from more than just my PN address?

[#2]

Spammers frequently pick a "return address" from their list, and send out hundreds of spams using that address.
Sounds like your email address got picked as the return address.
This effect is called Backscatter or Outscatter
Suffice to say, it will continue for perhaps a week or so, then subside.
P.

[#3]

Cheers; I did know how that worked but I was more interested if anyone at PN wanted to even attempt to trace the source.
I'm gonna delete the now 57 messages this evening (but I'm sure there'll be more).

[#4]

There is nothing sinister about it being your plus.com domain either. I have my main domain hosted elsewhere too & last night it got hit in the same way - roughly 600 returned undeliverable emails overnight.
It happens every now & then. Then it seems to go quiet for a while. My guess is that the spammers never use a single domain for too long because it's not in their interest to get any domain they want to use blacklisted.
My understanding is that tracing the source doesn't usually lead very far. I think it usually leads to some mug with an infected machine, rather than the people responsible.  I shouldn't be too rude in case one day I find out that someone has defeated my own security & I'm the one being the mug. 
I don't know what should be done to have a concerted attack on those responsible rather than just reacting passively with anti-spam defences. I assume those with more knowledge than I have considered this but not come up with a workable solution.