Sendmail script on edit

Sendmail script on edit

I am trying to create a script that sends an email if my Assigned_To field is changed.  So the conditions would be as follows.

If the Assigned_To field is changed then send an email to the user specified in the Assigned_To field.

I can get it to send an email on edit if the the Assigned_To field is equal to a certain user, but I only want the email sent if the Assigned_To was changed during the edit.  Otherwise every time a record is edited an email will be sent to the Assigned_To user even if it was a different field that was edited.

TIA