I maintain quite a few Twitter accounts – @labnol is my main account,@Howto Guides, @Podcast Gallery, @Hundred Zeros and some more.
If you are like me and have multiple accounts on Twitter, you are probably aware of the fact that it is not possible to associate the same email address with more than one Twitter account. Try it and Twitter will throw up an error saying – “Email has already been taken”.
Email Address for Twitter

Link Multiple Twitter Accounts with 1 Email

There’s however a simple workaround that will let you use the same email address with all your Twitter handles – the only condition is that you should be using a Gmail or Google Apps email address.
In Gmail, you can add a dot (.) anywhere in the username and all emails address to that new alias will still reach your mailbox. For instance, if your original email address is hello@gmail.com, any emails sent to he.llo@gmail.com or he.ll.o@gmail.com will land in your mailbox because Gmails ignores periods in the email username.
And that’s what you can use to trick Twitter. Twitter will consider hello@gmail and he.llo@gmail as two separate and valid email addresses even though they point to the same Gmail Inbox.
Update: Please do that note that you have to enable the catch-all option in your domain setting to use email aliases inside Google Apps. Thus it is a better option to use a free Gmail address for Twitter.
Another Workaround
When you open an account in Gmail, you automatically get another valid email address that uses the googlemail.com domain.
So if you only have two handles on twitter, you can use the gmail.com address with one handle and the googlemail.com address with the second handle.