You don't have to sign in with a Microsoft account to use Windows Live Mail, and you can add accounts and send and receive email without signing in. However, signing in to Mail lets you connect to other Microsoft services and also lets you use Mail features such as:
Photo email: If you create a photo email, your high-resolution photos are saved to Microsoft SkyDrive using the Microsoft account that you sign in with. Thumbnail photos are displayed in the message, which let your recipients see some or all of the photos before viewing the high-resolution photos online. This means that you can send more than a few photos in a message, and your recipients can see the photos online in a slide show and download them if they want to.
Messenger: If you have Messenger
installed on your computer, you can use Mail to see when a Messenger contact is available to start an instant messaging conversation.
Contact list: If you're signed in to Mail with a Microsoft account, you'll see the same contacts as you do in other Microsoft services such as Hotmail and Messenger. Any changes that you make to your contacts in Mail also happen in the other services. You can share your contact information on your Profile page, and you can ask to receive automatic updates when your friends change their contact information.
If you've never signed in to Mail with your Microsoft account, your contact list only contains the people that you've added to Mail directly and those who are added automatically after your reply to them thrice. Here's how you can change this setting:
In Mail, tap or click File, tap or click Options, and then tap or click Mail.
Tap or click the Send tab and then deselect the Automatically put people I reply to in my address book after the third reply checkbox.
Calendars: If you don't sign in, you can access your calendars only from the computers that you created them on. By signing in, your calendar is automatically imported into Mail, and any calendars that you've created in Mail are added to Calendar.
Anyone you share a Microsoft account with will be able to see your Mail accounts whether or not you're signed in. To prevent other people from accessing your Mail account, don’t share your Microsoft account with other people.
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