Is there an API (probably provided by Twitter but not necessarily) that will give me the Twitter username for each email address I give it?
Official response from Twitter on this issue is here - http://code.google.com/p/twitter-api/issues/detail?id=353
"This API method is offered in a closed beta at this time, and we are not accepting new partners. However, we're working on the long-term strategy for this method and will keep you in mind when we decide to open it up again. I am sorry for the inconvenience this may cause in the meantime, and please let me know if you have any other questions."
To my knowledge, the Twitter API doesn't expose or otherwise give access to the email address.
I understand your needs, as I also wish this were available, but I believe this is the decision Twitter went with.
来源：https://stackoverflow.com/questions/5995944/how-do-i-get-a-twitter-username-based-on-an-email-address