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Perfect email regex finally found

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Re: Perfect email regex finally found

#81

Post by tav »

davidu wrote: post #78
jrockway wrote: post #41

Earlier quoted context omitted.

What if I want to receive mail directly at my TLD?

Except it's not allowed... http://tools.ietf.org/html/rfc5321#section-2.3.5 RFC 5321 section 2.3.5 specifically prohibits TLDs from receiving email. Other RFCs back that up, actually including RFC5322 (not directly, but in wire format). That said, we see some TLDs run MX's. I think at least some portion of them sell the mail received there to spammers. Seriously.

Hey David,

You obviously know a lot more on this topic... but where exactly does it say in that section that TLDs are prohibited from receiving emails?

From my reading, it seems to suggest the opposite, e.g. "In the case of a top-level domain used by itself in an email address, a single string is used without any dots."

I've re-read that section many times and forgive me if I missed it — it's late! =)

People have been posting conflicting responses throughout this thread suggesting that TLDs can/cannot receive emails, and I'd really like to know which should be valid... thanks!

Re: Perfect email regex finally found

#82

Post by sjs »

mhartl wrote: post #79
sjs wrote: post #76

Earlier quoted context omitted.

The fact that you know the shortcuts for select all, copy, and paste puts you in the top percentile of users. Most people don't even know that's possible, and certainly not with keyboard shortcuts. (The point being that for most users the faster approach that requires less thinking is to type it twice. Sometimes I do things the "slow" or "long" way when coding because it doesn't require a mental shift from the task a…

That's true. My main point was the first one. The second point was mainly to illustrate that annoyance isn't hypothetical; I'm annoyed by an extra text box.

I agree they are annoying. I guess I'm just less annoyed than you are. Cmd-a Cmd-c Tab Cmd-v has a very negligible impact on the amount of keystrokes I make in a day. Typing my address again doesn't even make a real difference now that I think about it, 3 seconds or so.

Have you ever abandoned a sign-up because of the e-mail confirmation?

Re: Perfect email regex finally found

#84

Post by compay »

alnayyir wrote: post #3
andrewvc wrote: post #2

How ugly do non-regex based email validation functions look? I've never seen one, but I've always wondered if that was a more elegant solution.

Regex is the only real sensible way to validate strings until something better is found. Even if you just wrote code to do it manually, you'd really just be writing a verbose and poorly implemented finite state machine that globbed symbols together, which in the end, would just be inferior to writing a well tested Regex string. Regex can be easier to read if you have something do a graphical expansion for you. Otherw…

Roberto Ierusalimschy of Lua fame often uses this example of how PEGs (parsing expression grammars) can be much easier than regexps for some tasks.

http://lua-users.org/lists/lua-l/2009-10/msg00817.html

Re: Perfect email regex finally found

#85

Post by yammering »

sjs wrote: post #82
mhartl wrote: post #79

Earlier quoted context omitted.

That's true. My main point was the first one. The second point was mainly to illustrate that annoyance isn't hypothetical; I'm annoyed by an extra text box.

I agree they are annoying. I guess I'm just less annoyed than you are. Cmd-a Cmd-c Tab Cmd-v has a very negligible impact on the amount of keystrokes I make in a day. Typing my address again doesn't even make a real difference now that I think about it, 3 seconds or so. Have you ever abandoned a sign-up because of the e-mail confirmation?

Yes, there are many sites of all genres that don't require this. Don't underestimate it, do an A/B test sometime.

Re: Perfect email regex finally found

#86

Post by skoob »

"Now you have two problems."

Seriously, I can't think of a single good reason why you would want to check whether an email address is "valid". What you should be concerned about is whether or not the address works (and usually, can/does the person who just signed up actually read and reply to email to that address).

Hypothetically, if an invalid address works (due to bugs in mail systems) -- then it works, and the only problem with accepting such an address is that the bugs might get fixed. If an address is valid, there's no reason to assume that it will work or that it belongs to the person who signed up. It isn't even a good way of detecting typos; transpose two characters in an email address and it will most likely still pass your validation.

Re: Perfect email regex finally found

#87

Post by richardw »

percept wrote: post #14

I've accepted that it's best to treat people like grown-ups and if there's '@' and '.' and it's retyped then it passes. Someone can easily submit a fake name or phone number or street address, and e-mail's no different. If they get it wrong, intentionally or not, then they don't get their receipt, confirmation, validation link, etc. and I believe in most cases the incentive is there for them to get it right. In the r…

There are many other uses for this regex than registration systems. We have at least two situations where a staff member would type in a customer mail address, and some get it wrong. Confirming won't help, and getting it wrong costs lots of time to fix. Using a better regex costs very little.

Re: Perfect email regex finally found

#88

Post by dkubb »

billturner wrote: post #51
aphyr wrote: post #27

It's certainly more concise than my previous favorite, qtext = '[^\\x0d\\x22\\x5c\\x80-\\xff]' dtext = '[^\\x0d\\x5b-\\x5d\\x80-\\xff]' atom = '[^\\x00-\\x20\\x22\\x28\\x29\\x2c\\x2e\\x3a-' + '\\x3c\\x3e\\x40\\x5b-\\x5d\\x7f-\\xff]+' quoted_pair = '\\x5c[\\x00-\\x7f]' domain_literal = "\\x5b(?:#{dtext}|#{quoted_pair})*\\x5d" quoted_string = "\\x22(?:#{qtext}|#{quoted_pair})*\\x22" domain_ref = atom sub_domain = "(?:#…

This is the same one I've been using the last couple of years, and I wish I could remember where I first came across it.

From here maybe? http://tfletcher.com/lib/rfc822.rb

Re: Perfect email regex finally found

#89

Post by dkubb »

I've often wondered why we don't have any standardized test cases for email validation. A simple list of known good, and known bad addresses to use as test cases would really help.

You could almost make a game out of finding valid addresses that are not matched, or invalid addresses that are false positives, or optimizing candidate regexps. The list could be continuously growing as new variations are discovered, and tested against previously submitted candidate regexps.

Re: Perfect email regex finally found

#90

Post by Confusion »

percept wrote: post #14

I've accepted that it's best to treat people like grown-ups and if there's '@' and '.' and it's retyped then it passes. Someone can easily submit a fake name or phone number or street address, and e-mail's no different. If they get it wrong, intentionally or not, then they don't get their receipt, confirmation, validation link, etc. and I believe in most cases the incentive is there for them to get it right. In the r…

  If they get it wrong, intentionally or not, then they
  don't get their receipt, confirmation, validation link,
  etc. and I believe in most cases the incentive is there
  for them to get it right.
Well, I hope you have a large enough support team, because with any reasonable amount of customer growth, you'll soon be swamped with support emails that say "I didn't get my ..., where is it? You suck!". Validating the email address (which includes checking for common typos in domains) is a service that reduces frustration and the amount of customer support needed.
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