E-mail interviews are a new method of finding information but can be very useful, especially if you want to interview someone abroad or in a different time zone. The huge advantage of e-mail is that you can send someone a message and they will respond when they are able, saving you the trouble of having to track them down or wake them up. But many people have e-mail addresses they only look at every few days and some people don't answer their e-mails for weeks. if you don't hear from someone after a few hours, it might be worth ringing them.
E-mails are also useful in you can cut and paste the answer into your story ensuring that you don't accidentally Pervert what the person said. E-mails are great for contacting experts who you have discovered on web sites. Perhaps you are doing a story about BSE and its possible effects on human health. You are bound to find a web site with the names of a number of experts. You can then e-mail them all and.hopefully get some very usable quotes. Tracking down half-a-dozen university professors from all around the world by phone would take ages, but a group e-mail to addresses found on a web site is the work of a few minutes and can reap great results. Don't forget to make it clear you intend to use the results for publication. This is one time when you really have to be specific so that you are sure the interviewee understands how you intend to use their answer.
Always ask a string of questions in your initial e-mail. If you then have further questions, deal with those when you get a response. This saves a ping-pong approach that is long-winded by e-mail. It is better to be general so that the interviewee can give a wide-ranging answer. E-mail interviews are of less use for the 'How do you feel now that it's all over?' type question than the technically-based question about how something works. if you want to interview the victim of a rail crash, go and visit them. If you want to ask a professor of engineering about metal fatigue in rails, then e-mail may be the easiest method.