Four useful things to know about email addresses

I was talking to someone the other day and I mentioned a common email address hack I use a lot that he had no idea about. Realizing that, I thought of a few other bits of uncommon knowledge about email addresses that may be of interest to the world.

  1. Things after a + in an email address are ignored by email protocol. What this means is that will receive messages that are sent to This has a couple real perks:
    • Don’t trust that the service you’re signing up for is going to distribute its email list? (Or just curious?) Sign up as and you’ll be better able to tell who’s responsible for your spam.
    • In a more positive way, the above can also be useful for email filtering. The specifics of that are way beyond what I want to go into, but you can more easily find all your email from Press Up if you’ve got +pressup listed right there in the To: address.
    • Finally, you can use this the way I was—to test services that require unique email addresses. You may not be sure if you’ve tried that third email address you save for situations like that and you barely remember how to log in to, and you don’t really want to log in there to see if it works anyway. Use instead and their emails will end up in your regular inbox and won’t be blocked for uniqueness.

    There is one thing worth noting: while the email protocol always works effectively with +, some forwarding services (which might send all email to to, for example) don’t recognize the equivalence of and While they should, we’re probably wasting our time fighting gravity there, so unless you’re sure it’ll work it’s probably best to steer clear of the plus trick when a forwarding address is involved.

  2. Email is case-insensitive. works perfectly well to deliver to your typical address. The plus is a better system overall, but you could potentially use this for some of the filtering and sleuthing stuff listed above. But it’s far more useful to know so that if you think that looks better on your business card you can use it and not worry about mail getting lost.
  3. In Google’s Gmail, and only in Gmail, is identical to both and Same basic rule as the above, it could be a filter for you, but not a great one. It’s mostly nice as a way to break up your username on your business card, resume, etc.
  4. Finally, this is something most people should know by now, but since I’m making a list I’ll include it. Email is *very* easy to spoof. I can quickly send an email to your inbox that looks like I’m Barack Obama, Bill Gates, or Mark Zuckerberg. Or, less likely to raise you suspicion, an agent from your bank, broker, or other institution with your personal information. Never trust any email based solely on the listed sender and recipient. If it doesn’t look and sound like an official communication from the source it claims to be from, it probably isn’t.

About David Hayes

David likes learning, solving hard problems, and teaching. He bikes a lot, and lives in (and loves) Colorado. You can find him on Twitter as @davidbhayes and check out his latest hobby-project, Quodid, a monument to his love for pithy bits of wisdom.

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