Outlook API Integration Button

I need a custom button integrated into MS Outlook 2016 (64/32 bit) on Windows. When pressed, this button should display a popup allowing me to multiselect email addresses from all my contacts. The selected addresses, along with the email's HTML body and date, should then be sent to a specified API.

Requirements:
- Popup for multiselect email addresses
- Send to API: html body, date, email(s)
- Config page to add OAuth2 token and API URL
- Include a test connection button on the config page

Ideal Skills:
- Experience with MS Outlook add-in development
- Familiarity with API integration
- Knowledge of OAuth2 authentication
- Proficient in creating Windows applications