mail service vs postal service

mail service and postal service both are nouns.

Word	Noun	Adjective	Verb	Adverb
mail service	Yes	No	No	No
postal service	Yes	No	No	No

As nouns, mail service and postal service are synonyms defined as:

mail service and postal service: the system whereby messages are transmitted via the post office

Other synonyms of mail service include mail, post.

mail service (noun)	postal service (noun)
the system whereby messages are transmitted via the post office	the system whereby messages are transmitted via the post office