While composing a mail, on clicking 'From' an option to send from other email address can be seen. Is there a MAPI callback which helps to populate the email addresses when 'From' drop down is clicked? Which is the MAPI callback called when 'From' field is clicked?
There are no callbacks. Outlook builds that list from the list of accounts, it then adds the one-off entries (marked with X) that the user explicitly added. That list is stored in the profile section.