I wouldn't use only a placeholder because of the browser support. Not all old browsers support the placeholder! Take a look to this Stackoverflow Question and to this article about placeholder support.
And I wouldn't use the term "Email ID". Many users are confused about the "ID". I also heard many stories about the confusion of the "Yahoo ID".
"Should I insert here an email or a username? Do I have a username on Yahoo?"
Just use "E-Mail". It is simple and clear for all users.
So for me the best practice is to use a label with "E-Mail" and a placeholder with an example Mail:
I found an interesting article about your question "Email or E-Mail".
It say that official you should use Email.
A group calling itself the Email Experience Council has declared the official term to be email.
But many famous companys (e.g Microsoft) use also E-Mail. And in my opinion, E-Mail looks even better for me.
But keep your own counse and take a look to the article by The Fiction Desk.
I think I found the mistery of E-Mail / email!
On the english wikipedia, there is a really interesting part about the spelling:
e-mail is the most common form in print, and is recommended by some
prominent journalistic and technical style guides. According to Corpus of Contemporary American English data, this is the
form that appears most frequently in edited, published American
English and British English writing.
email is the most common form used online, and is required by IETF Requests for Comment and working groups and increasingly by style guides. This spelling also appears in
mail was the form used in the original RFC. The service is referred to as mail and a single piece of electronic mail is called a message.
eMail, capitalizing only the letter M, was common among ARPANET users and the early developers of Unix, CMS, AppleLink, eWorld, AOL, GEnie, and Hotmail.
EMail is a traditional form that has been used in RFCs for the "Author's Address", and is expressly required "for historical reasons".
E-mail is sometimes used, capitalizing the initial letter E as in similar abbreviations like E-piano, E-guitar, A-bomb, H-bomb, and C-section.
And the reason why I like "E-Mail" the most is, that i'm from Switzerland, where I speak German. And in the German Dictionary, there is "E-Mail" the official version.