Wildcards can appear in the name or domain sections
               of an email address. The following are valid examples:
            
               - 
                  
name@*: Valid representation of the whole
                     name.
                
               - 
                  
*@domain.tld, name@*.tld: Valid representation
                     of the whole name or the domain (not the top level domain (TLD)). 
                
               - 
                  
*@*.tld: Valid representation of both the name
                     and the domain (not the TLD).
                
            
            Wildcards cannot appear in a subdomain or the top-level domain. Wildcards also cannot
               appear with
               other letters; they must appear alone. The following are invalid examples:
            
               - 
                  
name@domain.*.tld: Invalid representation of a subdomain.
                
               - 
                  
name@domain.*: Invalid representation of a TLD.
                
               - 
                  
*name@domain.tld: Invalid use in conjunction
                     with a name.