Yes, that is standard subaddressing but not all email providers support it (I've never heard of a Microsoft Exchange server supporting it). One problem with it is it exposes your real email address. Another problem, as the Wikipedia article notes, is there are a lot of inputs with poorly written validation that won't accept '+' as a valid email address character (they often only allow a-z, '.', and '@').
This is a standard and every semi-smart spammer can strip the "\+.+" part so it works only with legit websites that you want to handle in a special way.
another options is to buy a domain with a cpanel and set up a forwarder and filter to a specific folder in your secret main email account. The extra benefit here, since you own the domain, is that you can create a send identity of your arbitraryforwardingaddress@yourdomain.tld
Be careful with this. I once ordered something with Dell, and while their front-end system would accept my email address just fine, apparently one of their back-end systems choked on it, and not only did my order get stuck in limbo somewhere, but their customer service agents also couldn't easily fix it for me since their systems weren't able to handle this properly either.
I use this scheme. I have a separate account (x@example.com), were I only give addresses with aliases (x+N-RANDOM-LETTERS@example.com). There are of course broken sites, that do not allow + in the e-mail address. Also Bolt (bolt-rider.com) ignores the alias and just sends to the base address (x@example.com).
You can also add dots ('.') anywhere in a gmail address and still have it delivered. You can use an unary encoding of your random letters if necessary.
Probably works with other email providers too.