Secomapp use Amazon email service to send email to your affiliates. Using Amazon service, emails sent to your affiliate are with sender's email is: firstname.lastname@example.org as default. In this default option, when affiliate replies to an email, merchant cannot receive it.
If you want to set up so your email is used as sender's email, go to Settings section and click on Use your email as sender's email:
By activating that feature, not only merchant email would be displayed as sender's email when sending to affiliate, but when an affiliate reply to an email, merchant can also receive that reply.