In your Organisation Settings, you can specify the email address that is used to send email reminders:
If you’re the business owner it's best not to send overdue invoice reminders from your own email address.
It’s much more professional (and better for your customer relationships) if you send it from an alternative address, such as:

When a customer replies to an email reminder, their reply appears in the Contact History for the customer, so everyone can see the conversation:

In addition, CreditorWatch Collect users who are cc'd on the reminder can also reply. Their replies will appear in the conversation history for the customer.