There seem to be lots of forms on the web that when asking for you to enter your email address, ask you to enter it twice.
Now in the case of where you are asking someone to set a password it makes sense to have them enter it twice since with a password the field is obscured so that no one can easily see what has been entered into the field. With the password it makes perfect sense to have them enter it a second time to ensure that what was typed actually matches what they intended to type and does not contain a typo.
Presumably those who want you to enter your email address twice are doing so with the mistaken belief that since it prevents typos when you set a password that it will do the same when you enter an email address. The circumstances though are somewhat different and what is essential for entering new passwords may have the opposite effect to what is intended with email addresses.
To start with you need to ask what is so special about the email address that they ask you to enter that twice while only entering everything else once. If the person is likely to make a typo and if getting them to enter it twice would prevent the typo then surely they ought to be asking to have everything entered twice and not just the email address.
The thing is that since only password fields have their value concealed from casual view, it is far easier for the person typing the information in to visually check what they entered into each field than it is to get them to enter it a second time. The person can see what they typed as their email address and so can easily tell if they mistyped it without the inconvenience of having to type it a second time.
A lot of people like to keep the amount of typing of repetitive information to a minimum and so if a form asks for the password twice and the person seeing the form can actually be bothered with filling out a form that asks for the same information more than once they will most likely just copy what they typed into the first field and paste it into the second. They can't do that with a password because it is hidden so that it can't be copied. If their email address contained a typo when they first typed it then the copy they paste into the second field will contain the exact same typo and so the request to enter it twice will just inconvenience those people by getting them to use copy/paste (assuming that they don't decide to just ignore the stupid form in the first place and go elsewhere).
Additionally, since an email address is something that is quite often requested to be entered into forms, a lot of people will actually have their browser configured to make entering their email address into forms as easy as possible. Many browsers allow you to save common values to be automatically filled out into forms and the email address is likely to be one of those. So assuming that the person doesn't make a typo in their email address when they first sdave it in their browser (and thus deliver the wrong email address every time they need to enter it), it should just be a matter of a couple of key presses for them to enter their email address into any form field. When it only takes two key presses to enter any email address into a form where it is guaranteed to be the exact same address as is entered into every other form, it makes no sense whatsoever to ask the person to press those two keys a second time to enter their email address twice. The email address is probably the field where people are least likely to make typos in entering the information since it is such a common value to be needed and so is so likely to be stored in the browser itself to save rekeying it.
For those who try to keep their typing to a minimum the two or three extra key presses needed to enter their email address a second time may be just enough to make them decide to not bother with the form in the first place.
Including a second email address field in a form basically says that you have the following opinion of the people you expect to fill out the form.
Yes, asking people to type the info twice may catch a small percentage of typos from those visitors who actually type everything in every time that is is asked for and who obviously like typing the same thing over and over but it will also drive away a lot of people who will not bother filling in your form at all. There's no way of capturing actual numbers for how many people fall into either of these groups but I suspect that those who ignore the form because of it stupidly asking them to press an extra couple of keys is likely to be far greater than the number of people it detects as having made a typo in one or other copy of their email address.
This article written by Stephen Chapman, Felgall Pty Ltd.