I find that the quantity of email 'spam' messages I receive goes through cycles; for weeks I seem to get very few then, for a while, there is an absolute deluge - often coming to an end soon after I've heard a news report that some internet 'spam-merchant' from somewhere or other has been convicted and forced to cease and desist, at least for a while.
In the past 4 or 5 days I've noticed a HUGE upsurge of these messages, the vast majority being diverted into my 'spam folder' with a 'delete all' command getting rid of them all at once. Occasionally however, a genuine email gets diverted into my 'spam folder' so it is necessary for me to scan down the header titles of all these time-wasting messages, just to check that I don't delete something important. Yesterday I deleted something like 240 spam messages, so far today about 50 or 60!!
The latest bout of 'spam' seems to have adopted a common tactic, which I've seen before on occasion - the header title purports to be a message reporting that an email I have sent has been undeliverable and is therefore 'returned to sender'; I do send out emails on occasion, but only a few a day - on the other hand it is also true that occasionally a message I have sent has proved undeliverable because I have mis-typed the addressee's email address, or because that email address is no longer active. It is also possible that one or other of my machines has somehow (despite my firewalls and anti-virus software) been hijacked for nefarious purposes and that my address book is being used to send out messages - but I doubt this because I keep my anti-virus scripts well up to date.
In any case, I have always followed a pretty simple rule - I never open an email unless I am ABSOLUTELY SURE it is genuine. If I am in any doubt whatsoever about the provenance of an email I receive, I delete it, so all those 'return to sender' messages simply get deleted out of hand. Better that than I inadvertantly let some virus into my machine by opening a message I suspect might be genuine, but can't be absolutely sure about - inevitably therefore if I have sent an email message very recently which has for some reason proved undeliverable I will have deleted any advice received back about this. Perhaps once the current spate of these messages abates I may re-assess matters.