Redirect incoming mail to alias, to external mailaccount

I have made a ellen@mydomain.com and created a rule to Redirect all mails to an external gmail used by this person.

I have also done this for eric@mydomain.com etc

After running the rule, it runs subsequent rules , because an email could be sent to both eric and ellen.

Usually the mail is redirected with no trace in my inbox.

But sometimes a copy is left in my inbox.

This is a problem, because the mail could be private for ellen@mydomain.com.

Any ideas about why this happens and how to fix it?