Send from a shared mailbox

For Outlook 2016:

https://www.ucl.ac.uk/isd/how-to/adding-shared-mailbox-to-field-outlook-2016-for-windows

In Outlook web access:

1. Create new e-mail
2. Click on the three dots in the toolbar at the top, next to Discard
3. Click 'Show from'
4. Click 'From' that appears
5. Click 'Other e-mail address'
6. Enter the full e-mail address and press enter
7. Now you can click 'From' in any e-mail to select which mailbox to send that e-mail or appointment from.