At times you may want to ensure that the recipient acknowledged the email that you have sent, therefore in such state you may actually create the read receipts for the outgoing messages.
You may follow the below steps for Enable read receipts :
1) Login to Smartermail by accessing the URL http://mail.domainname/
2) Proceed to Setting
-> Account Setting
and tick on Enable read receipts by default
3) Save it
4) Once the recipient received the email from the sender, then he/she might see a read receipt is being requested as below: