I'm trying to set up my custom domain account, I got everything working but wanted to centralize everything so I can check it through my Gmail account.

I tried adding it through Gmail > Settings > Account > Add Another Email Address

and it came back an error of:

You must send through domainname SMTP servers when you send as  emailaddress@domainname . However, this functionality is not available for your account. Please contact your domain administrator for more information.

And yes i've turned on imap on my zoho account.

currently I'm using POP but can only receive.

Please advice