Follow the steps below to do this:

1. Create the e-mail to be sent (Do not attach the attachment file).
2. Use eMailMerge to send to people who do not need the attachment.
3. Once Wizard is completed the original e-mail you created will be shown again.
4. Attach the attachment file to this e-mail.
5. Use eMailMerge to send to people who do need the attachment.