Fix issue #9457 where test outbound email does not work when opened

[JackBuchanan]

If password is not set, get mailbox using smtp user email address

Description

See issue #9457

Motivation and Context

See issue #9457

How To Test This

See issue #9457

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Final checklist

• [x] My code follows the code style of this project found here.
• [ ] My change requires a change to the documentation.
• [x] I have read the How to Contribute guidelines.