CB has an excellent solution for this below. Cleaning up the input addresses on entry into the HIBP database before hashing, would handle the most variations. With the addition of recording which +tags were removed, and positions of periods, the data would be comprehensive with very little compromise.
It may make sense to hash both versions. E.g. "HIBP found an exact match" and "the following variations were found in breach database" are both useful.
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CB has an excellent solution for this below. Cleaning up the input addresses on entry into the HIBP database before hashing, would handle the most variations. With the addition of recording which +tags were removed, and positions of periods, the data would be comprehensive with very little compromise.
It may make sense to hash both versions. E.g. "HIBP found an exact match" and "the following variations were found in breach database" are both useful.