Completely optional. Like HN for example.

So if someone forgets their login details, they're basically screwed? Because I've used some sites like that, and they're a royal pain whenever something goes wrong. For example, TV Tropes didn't used to have a password reset, so every time something went wrong, you'd pretty much have to either register a new account or bug someone on the forums about it.

Same with another site I was on, except the usual solution was seemingly 'find one of the staff on another site they're a member of and send them a message there'. Made for a nice security hole too, since people could (and did) impersonate others and get given their accounts as a result.

You need some sort of email (or other contact information, like a phone number) simply so people can get their account details back in a semi secure way.

Agreed. Whenever I've made email addresses optional, it just means I can expect to do a bunch of manual "forgot my password" support. And it's hard to justify responding with "sorry, can't help you since you didn't input an email" when you're in the early stages of growth and your one active user's remember-me session finally expired.

These days I prefer to require an email address. That way, the few users that want to opt-out can insert a bogus one.

You can have a password reset feature, but it would be optional. If the person decides not to include their email, they would have to bug a mod who would maybe reinstate them. You could also use SMS or a twitter handle or even snail mail instead of requiring an email address.

It's not that obvious how to delegate out a task that involves giving someone full access to an account when they ask for it.

With an on-site "Contact Support" form, you can at least compare their IP address with historical login addresses. But that comes with its own weird problems like, for example, a sibling claiming their brother's account from the same household to read their juicy PMs or steal their credits or whatever. Or giving moderators access to more sensitive information and power than necessary.

Password reset being "optional" just means that people are going to use your support system for it when they eventually forget their password or the initial registration session expires. Reddit and HN have optional email while your new website's only user just forgot their password without an email address on file. What are you going to do when they ask for help off site?

And by the time you're fielding SMS and Twitter handle password resets, you may wonder why you didn't just put more emphasis on the email address input field. Now you're polishing your SMS or Twitter handle reset system that has far more narrow appeal/usage than an email system.

Of course, at the end of the day, it depends on the type of service you're operating. But "make email optional" is a trade-off, not universally good advice. Spend too much time in the HN echo chamber and you'll just do things that work against your users.

People can opt out via http://10minutemail.com/.

You'd rather share your phone number or home address than your email address?

Instead of hiding my identity from the site, maybe I'd rather hide my use of the site from my email provider.

They have access to every e-mail you send and receive, if you don't trust your e-mail provider to that extent you should probably change them.

I thought so too. But then people started forgetting their passwords, so i made email mandatory. People will rarely write down/take note of their password to a website that they "just want to check out".

If they just want to check your website out, why are you forcing them to choose a password anyway?

Indeed. People shouldn't have to choose a password the first time they use your site. Our login flow in the open source http://qbix.com/platform lets the user check out the site without having to go through signup -> go to email -> click confirmation link -> back to site -> choose a password -> recover context.

In fact, most of our app users don't even have to sign up! They are invited via sms or email, and given a link that works like a capability. Clicking that link established an account for them and they get a full experience right away, complete with all their followers (people who uploaded their address books and had their number or email in there).

This is instant engagement of the user.

We don't even require a password for when they download our native app. We just go to Safari and do an OAuth 2.0 flow with our own site and give an access token to the app. That access token can be for 100 years.

They only need a password when their cookie expires or if they want to access the site from another device.

In that case, it's good to have asked for the email address or phone number in the beginning. That's the user's identifier.

Our system also works with Facebook connect, etc. but that's not the coolest part. The coolest part is having the user choose their own Qbix app as the identity provider to authenticate with, so they can visit new sites and they are instantly greeted by name, find friends on there etc. without the site knowing anything about them on other sites. That's the holy grail :)

How do they prevent Sybil attacks and DOS?

Perhaps by limiting the rate at which password-free accounts can be created. If this limit is exceeded then the system switches back to creating user accounts in the normal way.

And what if they want a lot of users? How do they know which are legitimate?