I am not able to use my domain email as sender for emails in eM client

I have a registered domain for which I configured mail forwarding. So I have an email address @mydomain which is forwarded to my existing address that I use in eM client. But when I add my domain email as ‘alias’ so i can send emails with it as sender I get an error when I send the email. Any specific steps or settings needed for this to work ?

Who is the provider that your domain email is forwarded to?