"We are going to push back very hard on this and will likely need support at the highest levels when it comes time for the final negotiation," the employee writes.
The planemaker said some communications "raise questions" about Boeing's interactions with the Federal Aviation Administration (FAA) in connection with the simulator qualification process.
In releasing redacted versions of what it called "completely unacceptable" communications, Boeing said it was committed to transparency with the regulator.
Unredacted versions of the messages were turned over to the FAA and Congress in December.
House Transportation Committee Chairman Peter DeFazio, who has been investigating the MAX, said the messages "paint a deeply disturbing picture of the lengths Boeing was apparently willing to go to in order to evade scrutiny from regulators, flight crews, and the flying public, even as its own employees were sounding alarms internally."