[minxomat]

You can funnel mail with Gmail, too using extensions. Although some online forms incorrectly reject this. Looks like this: [e-mail]

[Eldt]

Those can be stripped out, and the email sold or whatever.

[lloeki]

This is called subadressing.

https://en.wikipedia.org/wiki/Email_address#Subaddressing

[spacehome]

This is too well known to be useful anymore.