Why does it matter? If I managed to acquire the 8.8.8.0/24 netblock, I might very well want to use 'user@8.8.8.8' as my e-mail address.
I don't see why it has any material affect on someone requesting e-mail addresses: if it's valid, then it's valid.
This seems to be an example of the misplaced sense of propriety with which people approach validating e-mail addresses -- that somehow, your job isn't just to help the user enter an address, but also to define what is and is not 'reasonable'.
Imagine if companies refused to accept "1 Infinite Loop" as a street address because it's clearly ridiculous. Except that it's Apple's actual street address.
The one user in 10,000 who actually uses an ip address as an email address can surely figure out why they're getting rejected. Of course, he'll probably go channel the Comic Book Guy and write a scathing post on his blog (Worst. Regexp. Ever.), but the normal people who use the service probably won't see that anyway.
Again, what material difference does it make to you?
Overzealously rejecting valid addresses is an application of subjective and inaccurate ideas about what addresses 'should' look like, and ignores the simple fact we've already mutually and formally defined valid address formats via the IETF RFCs.
> Again, why does this matter to you, other than some sort of misplaced sense of authoritarian aesthetics?
Yes! Great Comic Book Guy impression.
Why it matters is that for most smallish companies, you want to get something up that helps your users not do stupid stuff (†), but due to time and resource constraints, you're likely to end up with some kind of 80/20 solution. It'll work well in most cases, and fall down in some others. I would certainly agree with the idea that you not force people, but a nudge is probably going to save you money in increased user retention and fewer support hassles.
† - I once had a person ask why their emails to http://example.com were failing.
In that case, great junior engineer impression on your part.
Pedantry matters in complex interoperable systems, because otherwise they're not interoperable. This is why we have detailed standards documents on e-mail address formats.
> I would certainly agree with the idea that you not force people, but a nudge is probably going to save you money in increased user retention and fewer support hassles.
A 'nudge' isn't going to come from yet-another-broken-email-validation regexp. There's no need for an 80/20 solution; this just isn't that hard.
> † - I once had a person ask why their emails to http://somesite.com were failing.
That's not a valid e-mail address (as per RFC822).
The crappy regex solution is much faster than what you suggest, and will work 99.9% of the time. The time you spend doing it the right way will reduce your conversion rate because people will view your site as slow. In this case worse is better.
No, it's not. Every time you exclude a valid e-mail address, you lose or annoy a customer for no reason other than your own lack of understanding of the RFCs.
There are a number of steps that can be taken that don't involve broken regexps that filter out valid addresses. Please stop trying to justify doing it completely incorrectly.
I do see a misplaced sense of propriety here, and it's coming from you. Blocking a few valid email addresses in the service of helping most customers is just a business decision, not a moral issue.
For example: requiring shirt and shoes in a restaurant will block some customers from dining there. But it improves the experience for all the other diners, so it's a net win.
