At least initially, one must:
- Load up
adsiedit.msc, - Find a user object,
- Get its properties,
- Click on anything in the list,
- Press P on the keyboard,
- Scroll to
proxyAddressesand edit it, - Set the primary address as SMTP:email@domain.com (note the caps in the prefix),
- Set all alias(es) as smtp:email2@domain.com (note the lowercase prefix!).
In some environments, a new tab appears in ADUC which means you don’t have to go back to ADSI Edit, but this is not always the case.