What are you hoping to achieve with CustumErrorObj.pm (many would spell that "Custom..." btw) that you don't get with Error.pm in terms of inheritance?

You seem to be saying that you don't want your mailer/viewer/logger classes deriving from a common base class. It's not clear to me how you can avoid that unless what you really intend is to add an Error.pm like interface to each class independently. On the basis of the "If it walks like a duck and barks like a duck, it is a duck", you could add the appropriate members to each class and they will look to any interested code as though they are the appropriate sort of duck.

(See the threads Re: isa() on any scalar, Is "ref $date eq 'ARRAY'" wrong? and Re^2: RFC: Object::Proxy (or somesuch) for relevant ideas.)