You may have noticed e-mails sent from your Salesforce Org to have no reply in the From field as shown below.
The reason that Salesforce does this is to enable Sender ID compliance. Sender ID compliance enables the receiving e-mail server to authenticate the sending e-mail server. If your recipient organization has the Sender ID compliance feature turned on and your sending e-mail server doesn't comply with it your e-mails will not be delivered to your intended recipient. This feature is enabled by default in your Salesforce org and Salesforce recommends that you keep it enabled. Note that when your recipient replies to the e-mail it correctly goes back to the user who sent the e-mail – so in the example above the reply will go back to firstname.lastname@example.org and not email@example.com.
In some cases you may want to turn this feature off – maybe because your customers may get confused with the no-reply. To do this go to Setup->Email Administration->Deliverability and uncheck the Sender ID compliance checkbox as shown below.
Again, we do not recommend that you turn this feature off unless you have a compelling reason to do so. You can find additional details in online help.