Mail is related to Service. Service is related to Servant. 
Blow is the opposite of Breathe. Person wants (to) Breathe. Traveler is a type of Person. Companion is a type of Traveler. 
Mail <--RelatedTo--> Service <--RelatedTo--> Servant 
Blow <--Antonym--> Breathe <--Desires-- Person <--IsA-- Traveler <--IsA-- Companion 