32 votesrsteer commented
While Troy has positioned this service as free, perhaps his "number crunching" could come out differently if this particular use-case were a paid feature. It probably shouldn't be THAT hard, although it's complicated by the fact that e-mail providers offering this capability are using different delimiter characters and it looks like some add the extension *before* the base e-mail name while others add it *after*.
But the people who make use of these aliasing features have demonstrated a higher-than-average personal priority on managing spam, privacy, and security, and would probably be willing to pay a modest amount. If Troy recommended this approach to his users, that might increase its use and increase the number of people wanting to use it as a paid premium service here.
I take a slightly more time-consuming approach, which DOES work with HIBP: I have a personal domain registered with a domain registrar that offers unlimited e-mail aliases on registered domains. So for any websites that are at all sensitive or that I plan to use frequently, I create a unique e-mail @ my personal domain. For one-offs I use generic temporary addresses that change periodically. (Example: To submit this comment, I will enter my unique e-mail for UserVoice in the e-mail box below the comment-entry box!)