Hearsay is an out-of-court statement offered for its truth. Several exclusions and exceptions do the work in commercial litigation.
Party admissions are not hearsay at all in most systems. A statement by the opposing party, or by its agent or employee on a matter within the scope of the relationship while it existed, is admissible against it. This is the single most useful rule in a commercial case, and it covers most internal emails.
Business records, as above.
Present sense impression and excited utterance for contemporaneous accounts.
Then-existing state of mind, admissible to show intent, plan or motive — how a party’s contemporaneous statement of what it intended to do gets in.
Statements against interest by an unavailable declarant, contrary to their proprietary or pecuniary interest when made.
Recorded recollection, where a witness once knew the facts, now cannot recall them, and made or adopted an accurate record. Read into evidence but not received as an exhibit unless offered by the opponent.
Statements offered for a non-truth purpose are not hearsay: notice, effect on the listener, verbal acts such as the words of a contract, and the fact that a statement was made.