Set the PostMaster email address in Office365

5th February 2021

The PostMaster email address is required by ZeroSSL and other cloud services to verify that you own the domain in question.

Run Powershell as administrator

Set-ExecutionPolicy Unrestricted
warning = Y

Install-Module -Name ExchangeOnlineManagement -RequiredVersion 2.0.3
if Install-Module is not recognized you will need to install DotNetFramework 5.1+ see here

You will need to respond Yes to 2 prompts

$UserCredential = Get-Credential

make sure the credentials you enter have authority to admin the domain

Connect-ExchangeOnline -Credential $UserCredential -ShowProgress $true

Set-TransportConfig –ExternalPostmasterAddress postmaster@domain.com