Hi NickieDee,
I know how invoice reminders are essential to make sure you receive payment. We appreciate you for posting your concern here and I apologize for the delayed response.
The issue you're experiencing is due to internal preferences in Internet Explorer that currently lack an option for modification. Unfortunately, the only available workaround at this moment is to send the invoice reminders through a web browser. I encourage you to post this concern on the Ideas Exchange Boards for our developers' attention.
In the meantime, please feel free to reach out if you need assistance with any other matters.
Thanks,
Genreve