Today I fell prey to spammers in a new way - it seems they are able to get email addresses really easily and then send out gazillions of emails that purport to be from you, then you get gazillions of non-delivery notices because lots of email addresses get closed all the time. My ISP being fairly vigilant then blocked me! So I had to phone them to get re-instated.
One of the easiest ways spammers get email addresses is people who forward junk mail without deleting the previous addresses and/or who have enormous distribution lists. Since I always delete the former and use bcc for long distribution lists, I can only assume that my email address was picked up from someone else who is less pedantic.
No finger pointing, no names, no pack drill... just if you are forwarding emails or sending out things with long distribution lists please be careful about what the whole world can see.
Thank you Madasafish for sorting my problem quickly and cheerfully!