Make sure the email field on the active directory users is the same as the primary SMTP email address in exchange.
To check if this is the case use this powershell command:
Code:
get-mailbox -resultsize unlimited | Where-Object {$_.PrimarySMTPAddress -ne $_.WindowsEmailAddress} To fix all users use this SMTP command:
Code:
get-mailbox -resultsize unlimited | Where-Object {$_.PrimarySMTPAddress -ne $_.WindowsEmailAddress} | foreach { set-mailbox $_.identity -windowsemailaddress $_.primarySMTPAddress }