For anyone on iOS or MacOS, there’s Hide My EMail built into iCloud services. It generates an email address and automatically sets up forwarding to your iCloud account. You can add notes to remind you what it’s for. You can disable an address at anytime in the iCloud settings.
I had this issue - I was trying to cancel my Guardian online news subscription, and they make it painful. Insist the email must come from the address, they didn’t allow a code validating ownership etc, was a complete pain