A person is looking to return to the Outlook fold but has one problem:
Thunderbird allows me to have multiple identities on a single account. I know I can do different profiles in Outlook but at that point I might as well setup multiple accounts. Can it be done with an Exchange server account?
When you use POP3 or IMAP accounts, and you email host allows it, you can send mail from another email address by typing the address in the From field. Not all email hosts allow you to change the From address but if your email provider allows it, the message will be sent from that address.
Note that many mail providers will add your account name or email address in the header so spam or abusive messages can be traced. Others require you to add the addresses to your account and confirm you control the address before you can send from it.
If you don't see the From field on the message form enable it on the Options tab of an open message.
When you want to send from another address, expand the From menu and select Other Email Address and type the address in the field. The next time you want to send from that address you can select it from the list.
You can use this method the redirect email to another address and have them appear to be from the original sender. To do so, open the message and click Actions, Resend This Message then click Send.
Note: this will not work with Exchange or Outlook.com accounts. You need special Send As permissions to send from other addresses when you use Exchange Server mailboxes.
While there are ways to send from other addresses when you use Exchange, it's not much easier. You'll need to have a mail contact or distribution group in the AD and have send as permission on it.
While I'm on this topic, I'll mention again that the new Outlook.com supports sending from Outlook.com aliases from Outlook. While it's always been possible to select an alias in the web interface, Outlook always used the account address. In the new Outlook.com, type the alias address in the From field and send. The recipient will see the alias.