Hello,
As we understand, you need a single email containing all the users that meet the criteria. In this case, it can only be done using a report. You can use the built-in report, Soon-to-expire passwords (by default located in container Reports\All Reports\Users\Passwords). For details on how to schedule reports, see https://www.adaxes.com/help/ScheduleReports. For the report to take into account the required value of extensionAttribute1, replace this line in the report script
$criteria = New-AdmCriteria "user" {(mailboxType -ne "shared") -and (changePasswordAtLogon -ne $True) -and (passwordNeverExpires -ne $True) -and (smartCardRequired -ne $True)}
with the below one
$criteria = New-AdmCriteria "user" {(extensionAttribute1 -eq "My value") -and (mailboxType -ne "shared") -and (changePasswordAtLogon -ne $True) -and (passwordNeverExpires -ne $True) -and (smartCardRequired -ne $True)}