Some sites (incorrectly) detect plus signs as invalid in email addresses. A superior technique, which requires more set-up, is to own your own domain name and give aliases to each corporate sender. For example, I use a technique where I give concatenate the company name with a secret key and hash it, then concatenate THAT between the company name and the @ sign in my email address, to give a first part that looks like e.g. amazon-a1b2c3d4e5f6@ (but with the actual hash) in front of danq.me. Then I can use filters to let through only email aliases whose hashes match those generated by my secret key.

But you can’t do that with plain old GMail, I’m afraid. I’d already moved-on by the time I wrote this article, in 2017, but wanted to share the “plus sign” approach for those people it would help, on those sites it would help on. Good luck!