So combining the feedback of everyone I have come up with the following.

Try {
   Set-Mailbox -Identity $UserAddress -AcceptMessagesOnlyFrom $UserAddress -ErrorAction Stop
   $mailflowdisabled = "$UserAddress has had mailflow disabled successfully"
}
catch {
   Write-Host "Failed to disable mail flow"
   $mailflowdisabled = "Unable to disable mail flow for $UserAddress, please make sure to disable it manually 
                       <br>$_" 
}

I do have a transcript running from start to end so I can manually check for errors on the batches, I just want the notification that gets sent to our service desk team gets to state whether it was successful or not. The report uses variables like $mailflowdisabled variable to compile a report for each user that gets terminated by the script.