Explainer
What is an email alias?
An email alias is an extra email address that forwards everything it receives to your real inbox. You can give each site or service its own alias, see exactly which one a message was sent to, and switch off any alias that starts getting spam without changing your real address.
Why one per site
If a store leaks or sells your address, only that store's alias gets spam. You can see who leaked it and turn just that one off.
Aliases and replies
Good alias services let you reply through the alias, so your real address stays private in both directions.
Plus addressing is not the same
Adding +shop to your address is free, but spammers strip it off easily, and you cannot switch it off. A real alias is a separate address.
Quick answers
Is an alias a second inbox?
No. It is an address that forwards to the inbox you already use.
Can I use my own domain?
Yes, with a service that supports custom domains; then aliases look like [email protected].