Send From Alias in Apple Mail

Send From Alias in Apple Mail

So I created my primary account me@mydomain.com and I added an alias to it admin@mydomain.com. I imported e-mails from both addresses from my existing provider and then created a filter to move all e-mails sent to admin@mydomain.com to a separate folder.

If I now go to send an e-mail from within Zoho Mail, I can send it using either address.

However, I also need to be able to send from both addresses using Apple Mail on my Mac and on my iOS devices but I can't work out how to add admin@mydomain.com as the address to send from in these apps. I tried just adding a new SMTP server using the alias address but I still can't select that as the address to send from.

Any Ideas