Here are four regular expressions (often called regexes) that all validate the format of an email address. They have increasing degrees of complexity. The more complicated, the more accurate each is at matching only email addresses.

1. Dirt-simple approach

Here’s a regex that only requires a very basic xxxx@yyyy.zzz:

.+\@.+\..+

Upside: Dirt simple.

Downside: Even invalid email addresses like xxxx@yyyy.zzz, or even a@b.c, make it through.

2. Slightly more strict (but still simple) approach

Regular-Expressions.Info provides a basic email validation regex that tries to be a little smarter:

[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,4}

Upside: Only allows email address-friendly characters, restricts domain extension to only two to four characters.

Downside: It still allows many invalid email addresses, and misses some longer domain extensions (.museum, for example).

3. Specify all the domain extensions approach

Reddit user teye points to his regex, which only allows domain extensions that actually exist:

([a-z0-9][-a-z0-9_\+\.]*[a-z0-9])@([a-z0-9][-a-z0-9\.]*[a-z0-9]\.(arpa|root|aero|biz|cat|com|coop|edu|gov|info|int|jobs|mil|mobi|museum|name|net|org|pro|tel|travel|ac|ad|ae|af|ag|ai|al|am|an|ao|aq|ar|as|at|au|aw|ax|az|ba|bb|bd|be|bf|bg|bh|bi|bj|bm|bn|bo|br|bs|bt|bv|bw|by|bz|ca|cc|cd|cf|cg|ch|ci|ck|cl|cm|cn|co|cr|cu|cv|cx|cy|cz|de|dj|dk|dm|do|dz|ec|ee|eg|er|es|et|eu|fi|fj|fk|fm|fo|fr|ga|gb|gd|ge|gf|gg|gh|gi|gl|gm|gn|gp|gq|gr|gs|gt|gu|gw|gy|hk|hm|hn|hr|ht|hu|id|ie|il|im|in|io|iq|ir|is|it|je|jm|jo|jp|ke|kg|kh|ki|km|kn|kr|kw|ky|kz|la|lb|lc|li|lk|lr|ls|lt|lu|lv|ly|ma|mc|md|mg|mh|mk|ml|mm|mn|mo|mp|mq|mr|ms|mt|mu|mv|mw|mx|my|mz|na|nc|ne|nf|ng|ni|nl|no|np|nr|nu|nz|om|pa|pe|pf|pg|ph|pk|pl|pm|pn|pr|ps|pt|pw|py|qa|re|ro|ru|rw|sa|sb|sc|sd|se|sg|sh|si|sj|sk|sl|sm|sn|so|sr|st|su|sv|sy|sz|tc|td|tf|tg|th|tj|tk|tl|tm|tn|to|tp|tr|tt|tv|tw|tz|ua|ug|uk|um|us|uy|uz|va|vc|ve|vg|vi|vn|vu|wf|ws|ye|yt|yu|za|zm|zw)|([0-9]{1,3}\.{3}[0-9]{1,3}))

Upside: It doesn’t allow xxxx@yyyy.zzz!

Downside: Upkeep could be tough with this one. You’d have to update any time new domain extensions are announced. In fact, you already would need to add the .me extension.

4. Way complicated approach

A Perl module has a long regular expression based on the standard description of an email address. It’s so long (nearly 6,500 characters!) that I won’t include it here.

Upside: It’s complete.

Downside: It’s way complicated.

Meet in the middle approach

You’ll have to decide, if you haven’t already, which regular expression to use. Likely, you’ll choose somewhere in the middle of the examples we’ve given. Regular-Expressions.Info has a good run-down of the trade-offs of different approaches.

Have you already decided how to check email addresses? How do you do it?

[via Reddit]

See also:

• A New Tool Offers a Little Help with Regular Expressions
• June 1 Is Regular Expression Day
• Tutorial: Use Regex in Perl

Silvan Mühlemann decided to find the best way to safely publish an email address. He started his test almost two years ago and recently published the results.

Silvan created nine email addresses and use a different method of obfuscation–nine different ways of hiding the actual address. Of the methods he tested, three of the email addresses never received a spam message.

The simplest method is to add markup with display: none styling so it doesn’t show:

email@<span style="display: none">null</span>example.com

The other two methods are reversing backwards text with unicode declarations and simple ROT13 encoding using JavaScript to decode. Next on the list, receiving just a few spam emails, was the popular email AT example DOT com method. Silvan did not test the email-as-image method, one employed by Facebook on its profile pages.

These methods probably won’t work with a mailto: link for easy clicking. Still, they all allow copy-pasting, instead of laborious re-typing, so they’re worth a shot. And yes, I know you could just use a contact form, but isn’t that a little impersonal? I think so.

It’s alive! Mozilla has released the first alpha version of its upcoming Thunderbird 3.0, the company’s next-generation e-mail application. We don’t suggest you rush out and download it unless you’re a true early adopter; this release isn’t stable and lacks many of the features planned for Thunderbird 3′s final release.

This alpha release is primarily intended to let Thunderbird fans know that the project is alive and well and the team is working hard on the next version of the open source e-mail client. It’s also the first product to emerge from the newest entity within the Mozilla organization, Mozilla Messaging. The company was spun off this past winter in order to give more attention to the Thunderbird project, which had long lived under the shadow of the much more successful Firefox browser.

The feature set looks promising. However, one the most anticipated features of Thunderbird 3 – integration with Lightning, an extension that adds calendar functionality – isn’t available yet.

The OS X version of Thunderbird 3 is now a native Cocoa app, meaning it can integrate with the Mac OS X address book, a much-requested feature. Unfortunately that functionality doesn’t appear to available by default yet either, but if you want to turn it on and test it out, Bryan Clark has posted some instructions.

The most interesting-looking feature that is part of this alpha release is the ability to open messages in tabs, which looks like a fantastic way to keep frequently needed messages easily at hand.

There are some other new enhancements, too, like a new add-ons manager similar to the one found in Firefox 3, and a much-improved search tool for finding text within messages.

Like the soon-to-be-released Firefox 3, the next version of Thunderbird will use the Gecko 1.9 engine, enabling it to take advantage of some of the memory and speed improvements coming in Firefox 3. The only downside is that Thunderbird 3 will require Windows 2000 or better. Sorry Win 98 holdouts, Thunderbird 3 isn’t in your future.

It does have a cool code-name, though: Shredder!

[via Mozilla Links]

See Also:

• Trouble At The Henhouse: Thunderbird Loses Key Developers
• Mozilla Thunderbird Takes Wing
• Mozilla Resurrects Eudora E-mail Client
• It’s Sink or Swim Time for Mozilla Thunderbird

In January they lost a lot of friends when they mis-billed their customer base, then added insult to injury with an overly irreverent apology.

More upsetting to me is the host’s recent decision to make Procmail, the classic and powerful mail-filtering tool, unavailable to users, after providing it for years.

A few of my own web apps take instructions from users via email as an alternative to a web interface, and Procmail is part of that signal chain. That’s not uncommon these days. Fortunately my apps are hosted elsewhere.

Dreamhost is not replacing Procmail with Maildrop or Sieve or another non-proprietary tool. They’re replacing it with their own in-house filtering mechanism, which they plan — at some point — to make “more robust so [sic] mimic many common procmail jobs”.

Seems like a move away from good things like interoperability, portability, standardization, and giving your customers what they’ve come to expect.

See Also:

• Poll: What Do You Use to Sort Your E-mail?
• Can The Gov Shutdown A Website Without A Court Order?
• Dreamhost Blocking BitTorrent Again

Thanks to the Journal’s high profile, a fix is now expected in “a month or so.”

Last I heard, which was not terribly recently, Yahoo was running a modified version of Qmail as their back-end. (Please correct me if there’s more recent information.)

Qmail works with Maildir-style storage, in which each message is its own file in a directory. Having 55,000 files in a directory is not prohibitive. If they’re running a filesystem with a shortage of inodes, that might be a sticking point, but you’d think a large company offering unlimited e-mail would think of that. In one archive folder on my server I have 186,373 messages at the moment.

Qmail supports per-user storage quotas, too. Until your inbox-filling-up problem is sorted out, Yahoo, you may want to read this FAQ.

You might also want to read this one:

What exactly does unlimited storage mean?

Unlimited storage gives normal email account users like you an opportunity to not have to worry about hitting a storage limit.

Sorry, that was snide. Realistically, my guess as to what broke is the indexing of the messages, not the storage. Personally, I have a non-fatal but serious allergy to storing my data on computers to which I don’t have physical access.

See Also:

• Yahoo Mail To Offer Unlimited Storage Space

Perhaps predictably for me, a notorious centralizer of data, I do my filtering on my mail server. I’m currently in the process of migrating from Procmail to Sieve to do that job. I’ll let you all know how it goes.

The Gmail-driven rage for sorting with labels rather than folders is cool if that’s what you’re into; personally I like folders’ hierarchical nature, allowing me to have subsets and subsubsets of my mail.

How do you sort your email into folders/categories?

Its killer features include massive configurability, exquisite IMAP support (the IMAP developer community and the Alpine developer community overlap significantly), aggregate commands, and the quick non-GUI interface everyone loves. Remotely-stored configuration files and address books mean you can set your favorite settings once and then use them anywhere.

One of the biggest new features introduced with Alpine is Web-Alpine, a web-based e-mail client with all the features (and indeed the codebase) of Alpine. The development team received a grant in 2006 to spruce up the Web-Alpine interface. Just imagine: open-source software with a professionally designed interface!

Version 1.10 is basically a maturity release. It fixes a passel of bugs and adds just a few small features.

The computing and networking group at the University of Washington has released Alpine, an open-source e-mail client for the desktop and the web. It’s based on Pine, the ancient but rock solid text-based e-mail client also developed at UW.

You may remember Pine from your school’s computer lab, your dad’s old Windows 3.1 box or (if you’re like Epicenter’s Dylan Tweney) from when you last checked your mail. Though it’s been the choice of Unix power users for almost two decades, Pine is also remarkably easy to use and simple enough for just about anyone to pick up.

But Pine is a copyrighted work — UW owns it and felt that they had taken development as far as they could. Also, Pine’s license prevents the distribution of modified versions. So, the computing group at the school decided to re-work Pine’s code from the ground up and release it under version 2.0 of the Apache License.

And now we have Alpine, an open-source, fully customizable lightweight client that looks and acts like Pine, but has been almost completely rewritten. Also included in the Alpine package is a web-based version, which was previously only available to UW students.

So, if you’ve ever wanted to take a stab at building a better Gmail, here’s a great place to start.

[via Slashdot]

The recently relaunched Boxbe has unveiled a new e-mail spam fighting service. Borrowing some ideas from IM and social networking, Boxbe adds a privilege system to your inbox which allows you to create an e-mail "friends list," much like those on social sites. It’s designed to help narrow down your e-mail workflow so you can focus more closely on the people who matter to you.

Of course the biggest danger in battening down your e-mail hatches is that important messages won’t get through, but to get around that Boxbe has a few tricks up its sleeve.

There’s no need to change e-mail addresses to use the service. Boxbe works as a plug-in, adding its spam-fighting features right in your Yahoo Mail account or within Outlook. Plug-ins for Gmail, Apple Mail and other popular e-mail programs are expected soon.

Boxbe combines elements of a traditional challenge-response (C/R) e-mail system with niceties like dynamically updated whitelists drawn from your address book and sent message history to help stop spam and make sure you get only the messages you want.

Earlier this week I spoke with Thede Loder, co-founder and president of Boxbe, who believes “Boxbe allows you to treat your friends’ e-mail with the respect it deserves, and reject any message that tries to invade your inbox without an invitation from you.”

Here’s how it works for Yahoo Mail users:

1. Tell Boxbe your e-mail address and OK the plug-in to access your Yahoo account.
2. Boxbe will parse through your address book and sent messages to create a whitelist.
3. Incoming messages from addresses not on your whitelist are quarantined in a new Boxbe mailbox.
4. The senders of those message will receive an e-mail informing them that their message hasn’t reached you. There’s also a link to solve a CAPTCHA, if they do that the message is moved to your inbox (i.e. they’re a real person).
5. All of your quarantined messages are scored and ranked according to the likelihood that they are spam. Boxbe appends a number from one to ten at the beginning of each subject line.
6. Click of the subject line and you’ll see all your potential spam in a neatly organized list from most likely hits to least likely.
7. Each message in your Boxbe folder has an extra link to add the sender to your whitelist. If you tell Boxbe to add the sender, that person will always go direct to your inbox from that point on.

It’s worth noting that you can accomplish most of this on your own by chaining together your own whitelists, or by using tools like SpamAssassin, but those options are more time-consuming and require you to keep everything up to date. And as Loder points out, those are things the average user is likely to do.

“While it’s possible to glue together a number of techniques and get pretty good results if you’re a system admin, with Boxbe the set up is much easier.”

There’s also a pretty good chance Boxbe’s algorithms are going to be more successful than your hand-culled whitelists. “Boxbe uses a whitelist too,” says Loder, “the difference is, what do you do with the grey area? We offer a way to save those messages in one place, dynamically update the list and offer scoring to suggest the likelihood of a message being spam.”

One of the big problems with challenge response systems is that they place the burden of getting to your inbox on the sender. Often, the messages sent back themselves look like spam, which means your sender may never see them. This latter problem will likely grow as spammers continue to spoof C/R messages as a way to evade filters.

To minimize this effect, Boxbe uses both SPF and DKIM server verification tools to cut down on the “backscatter” of challenges sent out. Rather than challenging every unknown sender as traditional C/R systems do, Boxbe discards those messages that obviously got bounced around and are therefore most likely to be spam.

What raises Boxbe above competitors like SpamArrest? The integration with your webmail accounts. Using Boxbe is about as painless and simple as you’re going to find. And it’s portable, which means if you change addresses, your whitelist can come with you and senders won’t need to re-authenticate.

That said, there are a number of problems with challenge-response e-mail systems that you might want to consider before you jump in with both feet – C/R systems add a burden that your sender may choose to simply ignore. Mailing lists with thousands of members present a problem as well since all those senders will need to be in your whitelist. And, of course, challenges increase the bandwidth burden on your mail server.

In its current incarnation, Boxbe offers seamless integration with
Yahoo’s webmail interface and Microsoft Outlook on the desktop. But
Boxbe plans to expand its services to eventually include the same tight
integration with other popular options like Apple Mail, Gmail and more.

Personally, I’d like a way to integrate Boxbe’s services into Gmail, but without the C/R element. In other words, Boxbe is a great spam fighting and message filtering add-on, and while the C/R aspect won’t bother some people, given the amount of legitimate unsolicited e-mail I receive everyday, C/R creates more of a headache than it could hope to resolve.

[Thanks to e-mail guru Paul Adams for his help with this post]

Part of Gmail’s popularity lies in its plethora of options. Even if it isn’t your primary e-mail address, options like the ability to set multiple “from” addresses make it an easy way to manage all your mail accounts in one place.

But there’s one flaw in that solution: if you send mail from Gmail using a non-Gmail address, there’s no copy of the sent message stored in your primary e-mail account, which is why the GmailAutoBcc Greasemonkey script is incredibly handy.

The simple script automatically BCCs a selected address so you can keep copies of sent messages on your primary mail server even when you send them through Gmail.

There are two versions of the GmailAutoBcc script, one for the old and one for new version of Gmail, both of which you can grab from the author’s site.

Once installed, GmailAutoBcc will ask you for an email address to copy to and after that the script will automatically add that address to the BCC field of all your outgoing messages. There are options to prompt every time you send and a few other tweaks like using CC instead of BCC (in Firefox type about:config in the URL bar and then search for “gbcc” to set your preferences).

Perhaps the best of these additional options is the “MapFromAddress” setting which allows you to associate the copied address with a particular Gmail identity. In other words, you can copy to different addresses based on the address that you’re sending from.

When it comes to e-mail You can never have too many backups and GmailAutoBcc makes it easy to fill in the one gap in the common Gmail-as-a-backup solution.

GmailAutoBcc works in any browser that supports Greasemonkey.

[via Lifehacker]

See Also:

• Google Adds IMAP Support To GMail
• GMail Adds Official Greasemonkey Support
• Firefox Plug-in To Supercharge GMail
• GreaseKit: Greasemonkey Scripts For Safari And More