Not sure what tag to put this under, but I joined a company that did not have the email attribute filled in on the user property object. Below is a PowerShell script that I used to fill it in.

#Input Text file for multiple users at a time
$input = Get-Content .\test.txt
foreach($inst in $input){
Set-ADUser -Identity $inst -EmailAddress $inst@domain.com
}

#Single user addition
Set-ADUser -Identity testuser -EmailAddress testuser@domain.com