The highlights of JetBlue's baggage regulations for both domestic and international flights are as follows:

According to JetBlue's baggage policy, the airline will choose whether checked baggage or hand baggage can be brought on board based on the weight, size, and contents.

Hand luggage for JetBlue must be stored in the overhead bin or under the seat. The traveler is solely responsible for their hand baggage, per JetBlue's hand baggage policy.
Only the flight carrying the passenger will accept checked baggage from JetBlue.
Baggage delivered on board a JetBlue flight must contain a baggage identity tag and a tag with the passenger's name, address, flight number, and contact information.
No carrier will accept carry-on baggage that does not meet JetBlue's baggage and size limits.
According to JetBlue's flight change policy, if a passenger requests to change the date, time or destination of his flight, JetBlue's baggage policy may be changed to a new flight itinerary. In accordance with JetBlue's cancellation policy, baggage refunds will only apply to selected fares.
JetBlue Baggage Limits will not apply to the Limited Fare under any circumstances.
JetBlue luggage charges
Only additional checked bags picked up at the airport or within 24 hours of the scheduled flight's departure will be subject to the JetBlue baggage fee.
Looking for a deal on JetBlue luggage? Up to 2 pre-checked bags may be added for a $5 per checked bag discount.
Please be aware that JetBlue baggage charges are only reimbursed in the event that the entire flight reservation is canceled before the planned departure.

JetBlue's excess baggage policy
Below is JetBlue baggage information regarding excess baggage policy:

Each JetBlue checked baggage that exceeds the maximum free baggage allowance of 62 linear inches and weighs 50 pounds will be accepted for a fee of $150 per piece, one way.
Baggage exceeding 62 linear inches but not exceeding 80 linear inches will be accepted for a JetBlue baggage fee of $150 per piece, one way.
Baggage that weighs more than 50 pounds or 23 kg but not more than 100 pounds or 45 kg will be accepted as checked baggage for a JetBlue excess baggage fee of 150 USD per piece, one way.
Overweight, overweight and/or oversized baggage is not accepted on JetBlue flights to and/or from certain travel routes on certain dates.
Baggage over 80 linear inches and weighing more than 100 pounds or 45 kg will not be accepted by JetBlue as these dimensions are subject to JetBlue's baggage policy. JetBlue lost baggage overview
In the event of lost, delayed or severely damaged checked baggage, passengers will not be able to claim JetBlue baggage unless:

JetBlue-Lost-Baggage
Passengers must notify or claim JetBlue baggage and receive a JetBlue lost baggage status number no later than four hours after flight arrival. Passengers must submit a JetBlue lost/delayed baggage report receipt to the airline no later than 21 days after the event before claiming JetBlue baggage.

In case of lost baggage at JetBlue, passengers must file a claim within 30 days from the date of the incident.

Conclusion
If the booking is canceled at least two hours before the scheduled departure time, the JetBlue baggage fee will be refunded to the original form of payment. If you board the trip but do not check in baggage, JetBlue Airlines baggage fees are non-refundable. Only checked baggage replenished at the airport or within 24 hours prior to scheduled flight departure will be subject to JetBlue baggage fees.

https://sites.google.com/view/baggage-policy-of-jetblue/