Head over to this Link. Here you will find the place to add a friend through their Email based on the different Mail Services. But, if you 're thinking of adding too many people then it would be better that you create a contact file. For the people who don't know the easiest way to create a contact file, here it is:
- Open a New text document (.txt) in Notepad.
- Add all the email addresses separated by a comma (' , ').
- Now save that file with the extension .vcf
Simple yet effective! If you are not blocked from sending Friend Requests but still you get warnings like 'This Friend Request Can't Be Sent' then you can refer another trick which will help you in bypassing this error here.
There's more in TechAmy which will definitely help you in Facebook, just head over here.