I have *@kayode.co forwarded to kayode@kayode.co. I can only send from kayode@kayode.co and only if I configured my mail client properly because my account is

I have *@kayode.co forwarded to kayode@kayode.co. I can only send from kayode@kayode.co and only if I configured my mail client properly because my account is actually a fastmail.com address. Unconfigured, the mail client will send as the fastmail account.