Twitter, like many web services requires a different email address for each new account or Twitter handle. This is particularly troublesome when you're trying to run a Russian Bot-Net like me to overthrow the USA government. If you didn't know, Gmail ignores all "." in the email prefix. While the period is handy to demarcate the surname, it is handled as if it wasn't there.
That means that donald.j.trump@gmail.com is handled the same as donaldjtrump@gmail.com.
When setting up multiple Twitter accounts which rely on unique email addresses for authentication, you can fool it by interrupting your normal email address with a period or dot ".' and at this time Twitter will approve it as a unique email, which means you can get all of your notifications in one space.
Original article from Google's blog back in 2008: https://gmail.googleblog.com/2008/03/2-hidden-ways-to-get-more-from-your.html