For clarification, and to confirm that you are using a valid "From" address, look at your own e-mail address and base the "from" address on the same format. For example, if a users e-mail is firstname.lastname@example.org, then a valid e-mail address may be email@example.com.
NOTE: The e-mail address does not typically need to be valid, but rather in a valid format (ending in hostings.com, for example) or whatever the users e-mail ending is. In high security environments, the e-mail may be required to be valid. Again, this should be confirmed with the SMTP Server Administrator.