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dominicsayers
isemail
PHP2012–2023
dominicsayers / isemail

isemail

Checks an email address against the following RFCs: 3696, 1123, 4291, 5321, 5322

Communication & Social
Explore on GitHubRead Hacker News discussions
4Distinct people
5Mentions
0Explicit recommenders
309GitHub stars
REPOSITORY AT A GLANCE

What to know before exploring

What it is

Checks an email address against the following RFCs: 3696, 1123, 4291, 5321, 5322

GitHub

Where it is used

No documented product use has been verified yet.

What people are saying

No recommendation phrase was found in the indexed comments.

No classified warning is attached to this page. Read the discussions before treating silence as approval.

Also in these discussions

No other repository is repeatedly linked in the same discussions.

This week on Hacker News

Nov 7–Nov 14 UTC · Direct repository links and separately labeled related project stories. Indexed through 11/14/2026, 3:56:07 PM UTC.

No direct repository links were found in the indexed HN discussions over the past seven days. Older discussions are available below.

Mentions over time

HN mentions by year5 dated mentions

Observed mentions: 2012-11-16 15:33:11 UTC to 2023-02-23 00:34:00 UTC.

01232012-01-01 00:00:00 UTC to 2013-01-01 00:00:00 UTC (exclusive): 1 mentions; 0 submissions, 1 comments20122013-01-01 00:00:00 UTC to 2014-01-01 00:00:00 UTC (exclusive): 1 mentions; 0 submissions, 1 comments2014-01-01 00:00:00 UTC to 2015-01-01 00:00:00 UTC (exclusive): 0 mentions; 0 submissions, 0 comments2015-01-01 00:00:00 UTC to 2016-01-01 00:00:00 UTC (exclusive): 0 mentions; 0 submissions, 0 comments2016-01-01 00:00:00 UTC to 2017-01-01 00:00:00 UTC (exclusive): 0 mentions; 0 submissions, 0 comments2017-01-01 00:00:00 UTC to 2018-01-01 00:00:00 UTC (exclusive): 0 mentions; 0 submissions, 0 comments20172018-01-01 00:00:00 UTC to 2019-01-01 00:00:00 UTC (exclusive): 0 mentions; 0 submissions, 0 comments2019-01-01 00:00:00 UTC to 2020-01-01 00:00:00 UTC (exclusive): 0 mentions; 0 submissions, 0 comments2020-01-01 00:00:00 UTC to 2021-01-01 00:00:00 UTC (exclusive): 0 mentions; 0 submissions, 0 comments2021-01-01 00:00:00 UTC to 2022-01-01 00:00:00 UTC (exclusive): 0 mentions; 0 submissions, 0 comments2022-01-01 00:00:00 UTC to 2023-01-01 00:00:00 UTC (exclusive): 0 mentions; 0 submissions, 0 comments2023-01-01 00:00:00 UTC to 2024-01-01 00:00:00 UTC (exclusive): 3 mentions; 1 submissions, 2 comments2023

Counts come from the repository’s dated source evidence. Index cutoff: 2026-11-02 08:16:59 UTC.

View mention counts and date ranges
UTC ranges include their start and exclude their end. Select a period to filter the source evidence.
PeriodStart (UTC)End (exclusive, UTC)MentionsSubmissionsComments
20122012-01-01 00:00:00 UTC2013-01-01 00:00:00 UTC101
20132013-01-01 00:00:00 UTC2014-01-01 00:00:00 UTC101
20142014-01-01 00:00:00 UTC2015-01-01 00:00:00 UTC000
20152015-01-01 00:00:00 UTC2016-01-01 00:00:00 UTC000
20162016-01-01 00:00:00 UTC2017-01-01 00:00:00 UTC000
20172017-01-01 00:00:00 UTC2018-01-01 00:00:00 UTC000
20182018-01-01 00:00:00 UTC2019-01-01 00:00:00 UTC000
20192019-01-01 00:00:00 UTC2020-01-01 00:00:00 UTC000
20202020-01-01 00:00:00 UTC2021-01-01 00:00:00 UTC000
20212021-01-01 00:00:00 UTC2022-01-01 00:00:00 UTC000
20222022-01-01 00:00:00 UTC2023-01-01 00:00:00 UTC000
20232023-01-01 00:00:00 UTC2024-01-01 00:00:00 UTC312

What Hacker News says

5 sources
hn_throwaway_99·Feb 23, 2023
The code itself is very helpful and interesting, https://github.com/dominicsayers/isemail/blob/master/is_emai.... Point is that checking whether something is a valid email or not is 1179 lines long (I know there are a lot of comments). Particularly interesting is to look at all of the possible error conditions, and the fact that "whether a string is an email address" is not so much a binary yes-no, but the library provides a "likeliness threshold" option. Essentially just pointing out that checking if a string is/can be an email address is surprisingly complex.
In Is_email()
robomartin·Oct 14, 2013
Having gone up and down this problem a number of times it is my opinion that the only way to truly evaluate email address validity is with a fairly elaborate state-machine based approach that provides you with feedback as to what is wrong in order to decide how to deal with it (or not). Here's one example: https://github.com/dominicsayers/isemail The regex's floating around out there are horrible. Validating email addresses doesn't necessarily mean that you affect the user's experience. I think of it as an opportunity to avoid losing a potential customer due to a silly mistake. One such example would be a one page sign-up site where you are trying to collect the email addresses of those interested in your offering. In this context it is important to try and catch errors. You have a visitor who wants to keep in touch with you. He or
Read the rest
she mistypes the email address. If you don't detect it you might lose them forever. Granted, all errors are not detectable. If someone types jeo@example.com vs. joe@example.com there's precious little you can do about it in terms of automated detection. You can accept obviously bad email addresses, store them in your database and simply tag them as such. This is where ML or human intervention might be able to fix the problem or choose to discard it. Email list pollution can be dealt with in other ways, for example, if you use this list to reach out to prospective customers bad emails will simply bounce. In the end what is important is to avoid losing real potential customers as much as possible. I think a little software-based verification along with giving the user the opportunity to catch the mistake is enough. All the junk easily falls though the cracks of a multi-stage filter after the fact.
In How not to validate email addresses
xyzzy123·Nov 16, 2012
Note that the source for that is_email test (I hadn't seen the library before) is here: https://github.com/dominicsayers/isemail That library is very good for telling you exactly what's wrong with an email address, but looking through the logic, you can see that handling all the edge cases involves significant effort. It seems to me that this monomaniacal focus on RFC 822 / RFC 5??? compliance is missing the point a bit. That stuff is important if you're writing a mail client or a server, not so much for a signup form or web site use. I am going to stick my neck out and say that for the purposes of a signup form, emails should be server-side validated as: anyCharButNullOrAt@valid-looking-domain.com 1. You split the email address into a local part and a domain, at the @. 2. The local part is allowed to contain anything but null, or @. This
Read the rest
will keep all the people who go john.doe+furrylist@gmail.com happy. 3. The domain section is validated against length and dns charset (letters, numbers, hyphens, dots) and then checked against e.g. the mozilla public suffix list for a valid TLD. This prevents admin@[10.0.0.2] from receiving signup emails. 4. After that you can punt to your mailer, as long as you do not give any feedback to the users (aside from reciept or non-receipt of email) on the success of delivery or verification (to prevent spam / bruting). Just say "an email has been sent", or somesuch. Anyone with two @s in their email address ("foo@bar"@bar.com) or (foo\@bar@bar.com) is evil, and should not be encouraged. You have to draw the line somewhere, and that's where I draw it. One reason these people are not worth spending time on is because many common clients such as gmail won't let you send to such addresses in any case. Try it... Let's thank our stars we don't have to handle Unicode addresses yet...
In Regexp-based RFC822 email address validation

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