How to Send mail from an additional Exchange address or alias

Until Outlook 2013 you can have only one exchange account on your outlook profile there for the only way to add different “From” address is by adding additional POP3/IMAP account to the outlook profile with the same details as the exchange account creating to accounts with the same credential but since it is pop3 you can manipulate the “From” address:

• In your account settings, choose to add a new account and select to configure it manually.
• Choose for a POP3 account and fill out the server details. Ask your Exchange administrator if you do not know these.
  For most Exchange servers, the settings are as follows (port and encryption settings can be configured by clicking More Options…-> tab Advanced);

  Your Name:	Your display name
  E-mail Address:	The alias address of your Exchange mailbox
  Incoming mail server:	Name of the Exchange server For Office 365 accounts use: outlook.office365.com
  Outgoing mail server (SMTP):	Name of the Exchange server For Office 365 accounts use: smtp.office365.com
  Username:	yourdomain\username or UPN(email)
  SPA:	disabled
  Port number POP3:	995 or 110 (without encription)
  POP3 Encryption (SSL):	Enabled
  Port number SMTP:	587 (or 25 in non-default configurations)
  SMTP encryption:	TLS
  My outgoing server (SMTP) requires authentication:	Enabled

another option is to create AD Contact or Distribution Group. Exchange administrator could create a mail enabled Contact or Distribution Group in Active Directory. This would then hold the alias address and your Exchange administrator can set it to forward all the emails to your main address and provide your account with Send As rights for it.