SomeOtherAddress.com is a domain that I connect to the SimpleLogin.io service to mask my real email address. I use it when I need to sign up for a service that I may not intend to use long-term or for which I don't want my real email addressed spammed.
When someone writes to any email address @someotheraddress.com, the email gets forwarded to my real email account. If I reply to the message, it is sent back through SimpleLogin.io to the person who wrote to me. They never see my real address, so they cannot spam me.
Later, if I find that I do not want to do business with them or they refuse to stop spamming the @someotheraddress.com address, I simply turn off forwarding for them and never get their emails again.
SimpleLogin.io offers a free service that lets you mask your real address, but you have to pay them if you want to your your own domain (like I do with @SomeOtherAddress.com). The free service is good, but not as feature-rich as the paid service.