To its credit, with Outlook Microsoft makes it fairly easy to set the default account it will use for sending E-Mail messages.
Unfortunately there seems to be no way one can get Outlook to use the default account. In other words, it is probably impossible to set a default account that will work. All one can do is tell Outlook what you want, and it will remember that default, but one cannot get Outlook to use the default.
What a way to run a railroad!
Is there no way to get MS to follow its own documentation?
j. r. Allen