Designating Email Accounts for 3rd Party Software utilizing Outlook

[Hooobi]

I have a number of email accounts set up in Outlook and would like to configure Outlook or Peachtree such that when I choose to email a client through Peachtree, it will utilize a specific email account (e.g., billing@mycompany.com) as opposed to the default Outlook account (myname@yahoo.com).

Any advice appreciated!