Yes is even easier than that these days aswell with bots specifcally written and available to purchase that take the knowledge behind email spamming away from alot of the people who are doing it. Essentially all a modern day email spammer needs is a list of email addresses which can be harvested easily from the internet by another bot that can be purchased, or you can easily purchase lists.
Essentially all that has happened is the return and sender address email has been spoofed on a bunch of emails that have been sent by somebody, the ones that were sent to non existant or email servers with blocklists, filters in place have bounced back to that spoofed information. I am surprised this is the first time you have come across it is a common occurance.
Personally I use several email addresses and use them for different things like for forums etc I will use hotmail anything that has the potential to easily harvest email addresses or be potentially published on a website such as within a profile etc. Then I have several others that only go out for important things that I dont want spam sent to.
Setting up spam filters is always good, but if you work within the gambling or adult industy then it sucks as they tend to act more like a blacklist and will class almost all your valid emails as spam meaning you will have to whitelist all the domains you want to accept from.
Nothing to worry about though just delete them all.