I suggest you ...

Enable search and notifications for email addresses using the "+" syntax

A lot of people use a syntax such as troyhunt+foo@hotmail.com where foo is a unique identifier for the site. They do this so that if they begin getting spammed, they can identify the source their email came from.

At the moment, HIBP treats this is a totally unique email address so if I've search for the parent email address without the "+" syntax, it won't be found. This idea is to ensure that searches and notifications recognise the syntax and return addresses that are logically still the same account.

One thing HIBP would also need to do is specify which account alias was in the breach or paste. For example, I would want to know that it was troyhunt+bar@hotmail.com that was exposed in the XYZ breach.

Edit: Just to put the value of this into context, I've just run some stats on the Adobe breach. Of the the 152,989,508 rows in the dump, only 49,905 email addresses have a "+" in the address so that's 0.03% of entries. That number is also a bit high as it includes junk entries. I'm definitely not ruling this idea out - it's still planned - I just wanted to give a sense of how useful it would be.

Edit: To add to this idea, Robert's comment about a period in the email is also very valid. I'd want to be very clear about the ubiquity of this practice across mail providers, but it's certainly a good suggestion and worth further investigation.

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AdminTroy Hunt (CEO / Founder, Have I been pwned?) shared this idea  ·   ·  Flag idea as inappropriate…  ·  Admin →


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  • Graham Bull commented  ·   ·  Flag as inappropriate

    I've been using Gmail with pluses for years. It's annoying when sites don't support this - and there are still plenty of them.
    I'm now considering doing something like what Stephen Turner does - e.g. linkedin@example.com, without using pluses.
    Not as good as HIBP supporting pluses, but it does allow you to use HIBP's domain search facility.

  • Titus commented  ·   ·  Flag as inappropriate

    Ik have to check for every unique adres sperately. Why? My provider supplies instead of just the xxxx@dds.nl als o<enter_anything_here>@xxxx.dds.nl.

    Ik give any company it's "own" adress. I use it to automatically filter my email , move to folders, and block adresses that have been leaked. Also I can prove to a company that they are the breach.

    But as it is even more specific than + adressing, I have little hope for a functionality like <wildcard>@xxxx.dds.nl.

    I can imagine the possibility for abuse. Maybe this is acceptable when wildcard is only allowed when there are 3 parts after the @?

  • AdminTroy Hunt (CEO / Founder, Have I been pwned?) commented  ·   ·  Flag as inappropriate

    If everything after the + is stripped, that information is no longer available to the owner of the address. For example, if I load a spam list and someone used "+netflix" then they no longer know it came from Netflix. Yes, they've has to explicitly check that address but many people also have domain-wide searches and this would screw that up.

    In short, nothing yet has changed with this idea: the pattern is still at very close to 0% usage and the same barriers still exist.

  • Anonymous commented  ·   ·  Flag as inappropriate

    I'm not sure who loses information about where the breach came from. Could you clarify that?

    And I think that if you choose to implement a feature to check against these cases, you will have to do it on a provider by provider basis anyways. Like you mentioned earlier, some providers have different rules (I'll keep in mind that outlook also has this awesome feature).
    What about this?
    When checking out a breach, instead of just stripping when there's +syntax, you create another column, eg "base_email", and if the email uses + syntax and is from a provider that is known to use +syntax, assign a stripped version of the email, else just the normal email adress(or None)?
    And then later when you're sending out notifications, also check the base_email?

  • AdminTroy Hunt (CEO / Founder, Have I been pwned?) commented  ·   ·  Flag as inappropriate

    Then you lose the information about where the breach likely came from which in cases like the last breach, if very important to people. Plus, applying this to one sole email provider feels exceptionally dirty and misses the same pattern used by other providers (ie outlook.com).

  • Anonymous commented  ·   ·  Flag as inappropriate

    What if you just stripped everything after the "+" and maybe the dots, but only for gmail adresses?
    Since they're the largest email provider that actually ignores dots and everything after the plus(I think.)
    There is a possibility of getting multiple entries by doing so, because besides finding out who added you to a mailing list and filtering out, another use of the plus and dots is registering multiple accounts with the same email adres on 1 site.

  • seizedengine commented  ·   ·  Flag as inappropriate

    Adding my vote to this. Its completely understandable that it is a significant development effort for a very small percentage of people however that group would appreciate it greatly. I think the number of users who do plus aliasing is also a group that is strongly security aware and are more likely to be subscribers to HIBP. In fact in posting this comment I am using a plus aliased account.

  • Anonymous commented  ·   ·  Flag as inappropriate

    I think people who use + emails are both more likely to use haveibeenpwned and less likely to have their passwords compromised due to being more selective about the websites they use.

  • AdminTroy Hunt (CEO / Founder, Have I been pwned?) commented  ·   ·  Flag as inappropriate

    It's not that simple Paul, there's a lot of other downstream impact by now having more data in the database than was originally in the breach. There are other processes this feeds into not to mention the way it changes the search for the reasons I've already mentioned.

    At this point in time, the fact remains that this pattern is used by almost nobody based on the data I'm seeing in the breaches. I'll keep assessing it and I *would* like to do this at some point, but it'd be a very bad ROI on the effort right now.

  • Paul commented  ·   ·  Flag as inappropriate

    I feel like you're making this too hard. If the input is troyhunt+bar@hotmail.com then just load it into your database as troyhunt@hotmail.com. done. Easy peasy. Strip the + during search, too. If a user searches troyhunt+bar@hotmail.com, give them results for troyhut@hotmail.com (which includes all results from all aliases).

    Or if for data integrity you really want to keep the + addresses in the database, just load the address twice; once as troyhunt@hotmail.com and once as troyhunt+bar@hotmail.com (for the rare instances where a + is actually part of the e-mail).

    You said these are in there very rarey, so you won't be duplicating much data. And for users who use +addresses, the website is somewhat useless. The whole point of +addresses is they're throwaway. I create one on the spot and forget I created it. It's not possible for me to search for every +address I've used. I'd rather have results that are overly cautious (troy.hunt@hotmail.com AND/OR an alias of troy.hunt@hotmail.com was pwned) than just not have any clue if an alias I used was pwned.


    Alternatively, handle this on the search end. You allow domain owners to search for multiple addresses based on domain. Maybe if I prove I own troyhunt@hotmail.com then I can search for permutations (based on rules you setup). For gmail maybe you allow + and dot. For hotmail just +. Etc. If this is a rarely used feature then optimization probably isn't very important. Results could just come as a spreadsheet/json like the domain results do.


    Re: the frequency.... If I were a spammer, whenever I saw a +address I would strip off the + and everything after it anyway. If any processing was done on these dumps, that could make the + seem even rarer... I do think this is a rarely used feature, but it could be a percentage point or two more frequent than it seems.

  • Rob commented  ·   ·  Flag as inappropriate

    Hi Troy - first off thanks for the fantastic facility you provide via this website.

    Personally I use gmail accounts for most things. With regard to the placement of the ‘.’, I only use two variants - one without any, and one with them in to make the address more readable, so that's not a big deal for me; however, I make heavy use of ‘+ addressing’, not necessarily for major websites, but for things like forums, newsletters, sites I think may spam etc.

    I've been analyzing the haveibeenpwned report for our company domain. There are just over 1200 entries. Of those there are only 4 entries that are not included in the "Online Spambot" list, and those four are all genuine users.
    As a sample I've gone through all users starting with a "c", and at most 12 of 144 are potentially genuine. The vast majority of the rest look to be auto-generated, plus some invalid ones but based on real users' surnames.

    Based on those stats and also the unlikelihood of auto-generated spam email addresses being created with plus addressing, I therefore suspect any addresses that do contain plus addressing are very likely to be genuine accounts.

    Extracting and entering into the site all the plus variants of my email addresses from my password safe, and then on an ongoing basis adding new ones every time I sign up to a site could be quite onerous.

  • Stijn Crevits commented  ·   ·  Flag as inappropriate

    I too use the +string method to identify sites that leaked my email address to spam lists. So this ofcourse results in a long list of variations of email.address+string@provider.com.
    It would ofcourse be nice if I could receive HIBP notifications for all of them, without having to enter each of these email address permutations.

    But I can understand that this request results in some difficulties, as mentioned by others in the topic.

    To David's comments, it appears that the email provider of Brian Krebs DOES follow the spec to heart and differentiates between email addresses based on capitalization (see https://twitter.com/briankrebs/status/940362654434168833).
    However, the implementation of the spec differs between providers. As mentioned earlier, Google doesn't care about the periods, some providers (or sites) don't allow the use of + or other signs, ...

    The question for ignoring everything after a +-sign would be whether there are email providers who allow registering different email addresses based on the value behind the +-sign. I.e. could foobar+alice@provider.com be a different user than foobar+bob@gmail.com?

  • AdminTroy Hunt (CEO / Founder, Have I been pwned?) commented  ·   ·  Flag as inappropriate

    To David's comments, this shows how tricky the situation is; there's the spec, the practices by various mail providers and then the patterns people general use. I'm very cautious about making assumptions on these as they may not always hold true under all circumstances which then means ending up with a kludge of provider-specific hacks (i.e. always ignore the dot in Gmail addresses). I'm sure everyone can see the challenge and even if solved, there's still just that tiny percentage of people for whom it would make any difference at all.

  • David A Bacher commented  ·   ·  Flag as inappropriate

    Periods are significant in the local part of email addresses per RFC 3522 (https://tools.ietf.org/html/rfc5322#section-3.4.1).

    Email addresses are case sensitive, and period, plus and hyphen are significant characters.

    It's safe to assume that no sane system administrator is going to set up mailboxes that differ only incase, or where the local name is a bunch of quoted printable Emojis, etc. However, note that I used the word "sane" so there are probably thousands, maybe millions of systems doing it out there somewhere on the Internet. :P

    Also, hyphen is valid in the global DNS system, and so whatever you do -- don't just strip it from the whole address. That causes significant problems for users whose domains actually have a minus sign in them.

    But if you do this sort of normalization, easiest way is a set of regular expression substitutions based on the domain name. Since the local part is determined by the ISP in question, the rules have to vary and so you worry about the big guys.

  • Mike commented  ·   ·  Flag as inappropriate

    Well, if anyone would know it'd be you. Thanks for your willingness to engage!

  • AdminTroy Hunt (CEO / Founder, Have I been pwned?) commented  ·   ·  Flag as inappropriate

    Mike, you'd be surprised at how mainstream the HIBP user base is, largely because of how much press it gets in the general media. But even if I was off by a factor of 10 (which I'm almost certainly not), in an incident like River City Media, the percentage of people using this pattern rounds to 0% even with 2 decimal points of precision!

    I understand this is important to the people using it, but I need to look at the impact from the effort and at present, it remains near non-existent.

  • Mike commented  ·   ·  Flag as inappropriate

    Troy, I'd argue that your user base is not represented by the data in breaches. Obviously a very small percentage of people in the world use a + in their email (as evidenced by your research). But, I'd wager that a much larger percentage of people using HIBP do.

    I assume your hope is that even the most technologically illiterate users come to HIBP. However, I imagine that most users are already security conscious and don't fall into that group.

  • AdminTroy Hunt (CEO / Founder, Have I been pwned?) commented  ·   ·  Flag as inappropriate

    Since Antonios has left a comment and I've also just loaded the largest data set ever into HIBP, I thought I'd add a current figure to the discussion here:

    0.0038% was the percentage of people with a + in their email address in the River City Media spam list. 1 in every 26k people is a hard ROI to justify when there's a fair bit of work to invest!

    I'll keep monitoring the use of this pattern, but as of now, it remains *exceptionally* rare.

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