Are you sure it is not a restrictive measurement by gmail? do you get the same error if you send from a non-gmail address? (for instance, from your ISP)
Are you sure you have set up mail for that domain correctly? (MX records, DKIM etc…)
Are you sure it is not a restrictive measurement by gmail? do you get the same error if you send from a non-gmail address? (for instance, from your ISP)
Are you sure you have set up mail for that domain correctly? (MX records, DKIM etc…)