As someone who has habitually used +addresses since creating my Gmail account, this would be a very desirable feature for me (as would Gmail's "optional dot", thanks to poorly-written email scraping bots). Using a suffixed address for each account I create (e.g. "[me]+uservoice@gmail.com" for this site) has allowed me to track bad actors who share my email address without my consent.
I understand that there are some technical challenges here, as both "+" and "." aren't indicated to have special behavior in any standard I'm aware of. Any email host which assigns special meaning to them is therefore an exception. This could potentially be managed by maintaining a list of hosts which are known to assign special meaning to characters, though that would be an additional (if hopefully small) maintenance burden for HIBP.
Alternatively, the plus sign specifically could be assumed to always have the special meaning of introducing an "irrelevant" postfix. While it's certainly not true of *all* email hosts, there are even today a large number of site which disallow that character appearing in an email address at all, either because they incorrectly believe that it's an invalid character or simply due to encoding issues. Add to that the fact that Gmail's use of the character has become popular among other hosts as well and it may be reasonable to simply assume that "+" only appears in email addresses as a special character.
Ben Blank
As someone who has habitually used +addresses since creating my Gmail account, this would be a very desirable feature for me (as would Gmail's "optional dot", thanks to poorly-written email scraping bots). Using a suffixed address for each account I create (e.g. "[me]+uservoice@gmail.com" for this site) has allowed me to track bad actors who share my email address without my consent.
I understand that there are some technical challenges here, as both "+" and "." aren't indicated to have special behavior in any standard I'm aware of. Any email host which assigns special meaning to them is therefore an exception. This could potentially be managed by maintaining a list of hosts which are known to assign special meaning to characters, though that would be an additional (if hopefully small) maintenance burden for HIBP.
Alternatively, the plus sign specifically could be assumed to always have the special meaning of introducing an "irrelevant" postfix. While it's certainly not true of *all* email hosts, there are even today a large number of site which disallow that character appearing in an email address at all, either because they incorrectly believe that it's an invalid character or simply due to encoding issues. Add to that the fact that Gmail's use of the character has become popular among other hosts as well and it may be reasonable to simply assume that "+" only appears in email addresses as a special character.