I'm doing this query:

     SELECT
          ID, Name, Email_Domain__c
    	FROM
          Contact
    		GROUP BY Email_Domain__c

And I'm getting this error

> MALFORMED_QUERY: GROUP BY Email_Domain__c ^ ERROR at Row:5:Column:12
> field 'Email_Domain__c' can not be grouped in a query call

Is there a way form to `GROUP BY` a custom field?

**UPDATE**

When I check this field in workbench, it has these 2 properties

    calculatedFormula: RIGHT(Email,((LEN(Email)-(FIND("@",Email)))))
    
    groupable: false