This info is somewhat dated and incomplete.

See also: https://www.lifewire.com/send-email-with-any-from-address-outlook-1173706

When using POP or IMAP accounts (ie. not with MS Exchange Server), you have to create another account in your Outlook configuration for the new identity. Then, depending on your Outlook version, you are presented with another 'From' address or an 'Account' selection to choose your 'From' identity.

1. Create a new Outlook account that is a duplicate of your original account.
2. Change at least the e-mail address (which also changes the Reply To address).
3. Configure the new account not to Send/Receive mail (it's actually the same account and will only complicate things if Send/Receive is left enabled) (Outlook 2010 shown, other versions similar):
   • Click Send/Receive (tab) → Send/Receive Groups → Define Send/Receive Groups → All Accounts → Edit
   • Select (highlight) the new account on the left
   • Deselect the “Include the Selected Account In This Group”
   • Save
4. When creating a new message, Click the From button to select the identity.
   • The “From” field is normally hidden. Expose it by choosing it from the Options menu when creating a new message.
5. Verify the clicking the Send/Receive button does NOT check the same account twice.

Microsoft Exchange makes identity management possible with Outlook.

See the properties “Send As” vs. “Send on Behalf of”.

http://www.howto-outlook.com/faq/aliases.htm

The previous link has useful information on products from this company:

http://www.ivasoft.com/

http://www.howto-outlook.com/faq/aliases.htm

Using info from above link this is done entirely in Cloud Panel.

• Login to CloudPanel → Resellers → Companies → Company with user needing identies → Exchange → Microsoft Exchange → Distribution Groups → Add New → Distribution Group
• For Name* use the name of the person using the identity. This will be the name displayed to the recipient of the emails.
• If needing more than one use a different name (Last, First or Middle initial, etc.) for additional Distribution groups
• For Email use the email the sender wants to be using
• On the Managed by use the same user
• Members tab add same user
• Permissions tab add same user to Send access
• Delivery Management set for Senders inside and outside…
• Click Save
• Have user log out and back in as they have been added to a new group

This will not start working immediately. I suggest waiting 2 hours to test. I found it throws a user not authorized error.

• In outlook start a new message
• To expose the From field click Options → From
• Click the carat next to From → Other E-mail Address…
• Fill the From field with the email address desired → OK

Do this for all identities desired. After doing this once they will be available when clicking the From carat.

• Login to OWA and start a new email
• Click the ellipses in the top menu → Show From
• Click the carat next to From
• If you have populated the From with other identities they will show