All social features (theChat, Mail, and Friends options) can be accessed through the social hub. You can search and add friends, as well as send private messages to players on your friends list.
Can We Block Mails?
If you block a player, you will never see chat or private messages from them.
How Do I Prevent Friend Requests and Alliance Invites?
You have the ability to turn invitations off and on from the settings menu.
From the home screen, tap the gear icon in the top-left corner of the screen, and you will access your settings menu. Tap on the CHAT tab at the top, then tap the checkbox next to which invite that you would like to turn off (alliance invites or friend requests).