He wore a chain mail to protect himself in battle.

He wore a coat of mail for protection.

I prefer to do mail order shopping because it's convenient.

I found a letter in the mail slot.

I prefer mail-order shopping because it is convenient.

I need to e-mail my boss about the project.

I received an email from the mailing list.

I received a package in the mailbag.

I found a letter in the mailbox.