If you have configured SliQ to use Microsoft Outlook to send emails then your emails will be sent from whichever is the default email account set up in Outlook. If you have several email accounts set in Outlook then you may find that your business invoices are sent from a different email, e.g. your personal email. This means that when your customers reply to your emails their replies get sent to your personal email address.
To make sure your invoices are sent from your business email, you need to make sure Microsoft Outlook is using your business email account as its default. To check or change the default email account in Microsoft Outlook, see setting the default email account