Gmail doesn't allow you to do email merges, which is a huge time saver when you need to send the same email to dozens of people!
You need a MS Outlook to do this.
Important considerations:
This is not selected by default! You need to change this setting to be sure that the 'send from' is coming from the email address you want to use (assuming you have multiple email accounts in outlook).
Set the default account in 'account settings' to the one you want to send 'from' and then choose options to set the default send:
Next, go into Options and Mail to be sure 'Always use the default account when composing new messages' is checked (it may not be by default):