I changed the from email address by setting the OrgWideAddress; but still the email's from address says
firstname.lastname@example.org on behalf of testEmail@test.com
Can it be changed to a regular email name without "on behalf of"?
There is a salesforce knowledge article that covers this. Go to Setup > Administration Setup > Email Administration > Deliverability Under the email security compliance section, turn off the SenderID compliance checkbox, and now email vendor / clients will not include the "Send on behalf of".
Please keep in mind, by enable to comply with Sender ID email protocols. This declares salesforce.com emails as coming from an authorized IP address.
An alternative as well is to enable Email Relaying. What is Email Relaying? Email relaying is using an email server to send email that did not originate on the email server. Companies set up email relaying to:
You can set up email relaying for Salesforce-generated email by configuring Salesforce to automatically route email through your company's Simple Mail Transfer Protocol (SMTP) server.
For more information on how to setup Email Relay Please Click Me