Received email shows an incorrect email address in 'To' field

Emails send fine – but once received, while the ‘From’ field is correct (it displays our admin email address), the ‘To’ field displays a non-existent email address that it’s created by mashing together an old user name that we had in the system and adding it on to our domain (e.g. we had old admin named steve evans. He no longer exists in our system; the emails users are receiving show our correct admin address in the ‘From’ field but in the ‘To’ field it displays “Steve Evans ([email protected])” — even though that was never his email address.

Even more confusingly, when a user tries to reply to the email, instead of their reply goin to the address the email came from, it tries to send their reply to the incorrect ([email protected]) email address.

We are using ‘WordPress default email service (wp_mail)” as the email service so that recipients can be hidden in the BCC field.

https://www.ads-software.com/plugins/events-manager-email-users/