How to Edit Exchange Authentication Policies in Powershell

Following these instructions, you can edit Exchange Authentication Policies:  

First, connect to the  Exchange Online PowerShell module from Microsoft here,  and run the Get-AuthenticationPolicy command.

If you see a blank return, it means there is no policy and you need to configure one.  

Create a new authentication policy named Allow Basic Auth.  
 New-AuthenticationPolicy -Name "Allow Basic Auth"

To enable AllowBasicAuthPowershell and AllowBasicAuthWebService in the new authentication policy:  
Set-AuthenticationPolicy -Identity "Allow Basic Auth" -AllowBasicAuthPowershell

Set-AuthenticationPolicy -Identity "Allow Basic Auth" -AllowBasicAuthWebService

Assign this policy to the Virtual Systems service account by replacing <UserIdentity> with the Virtual Systems Veeam O365 Backup account:
 

Set- User -Identity - <UserIdentity> -AuthenticationPolicy "Allow Basic Auth" 

 
 
If you have a policy but true is not listed for AllowBasicAuthPowershell andAllowBasicAuthWebService, update with the following PowerShell cmdlets to update your policy.  

Set-AuthenticationPolicy -Identity “name of your authentication policy” -AllowBasicAuthPowershell 

Set-AuthenticationPolicy -Identity "name of your authentication policy” -AllowBasicAuthWebService 

 
Assign this policy to theVirtual Systems Veeam O365 Backup account, replacing <UserIdentity> with theVirtual Systems Veeam O365 Backup account.  
 

Set-User -Identity <UserIdentity> -AuthenticationPolicy "name of your authentication policy"