Are you by any chance a Talktalk customer?
A few years ago Talktalk was hacked into and e-mail addresses (mine included) were among the data stolen.
As a result over a period of several weeks or months I started to receive spam/scam e-mails which at their peak numbered 30 or 40 a day. Most addressed me as "Dear xxxxxxxx" using my Talktalk user name but they eventually died down and stopped. That is until recently.
For the past 4 or 5 weeks I have been receiving e-mails which sound similar to yours all offering vouchers for among others, Sainsburys, Morrisons, Asda, John Lewis and all include among the sender's details "via asda-announce-bounces mail.........". Currently I am receiving perhaps up to 3 or 4 most days and as before all of them address me using my Talktalk user name.
My guess is that the e-mail addresses obtained from the original hacking have been re-circulated and brought into use again. After the hacking incident I opened a second e-mail address with Talktalk but it is only the original one that has received these messages.