Create the availability address space in Office 365
Open a Powershell command and use the following commands (will need to be modified for the environment) to create this:
$Credential = Get-Credential
$Session = New-PSSession -Credential $Credential -AllowRedirection -ConnectionUri https://ps.outlook.com/PowerShell -Authentication Basic -ConfigurationName Microsoft.Exchange
Import-PSSession $Session
New-AvailabilityConfig –OrgWideAccount "<YourO365Administrator>"<----- Replace <YourO365Administrator> with your Office 365 admin account.
Add-AvailabilityAddressSpace -AccessMethod OrgWideFB -ForestName -Credentials $Credential –TargetAutodiscoverEpr 'https://autodiscover.<YourSMTPDomain>/autodiscover/autodiscover.xml' <----- Replace <YourSMTPDomain> with your SMTP domain name.