The exchange centered on the 737 Max's angle of attack (AOA) indicator, a feature only available as a paid-for extra.
All 371 Boeing 737 Max airliners have been grounded since March 13 after the crashes of Lion Air Flight JT610 and Ethiopian Airlines Flight ET302.
Boeing made optional a feature on its 737 MAX planes that would have alerted pilots when a key sensor was providing faulty information.
The Verge reported that Boeing deployed account representatives to convince airlines to remain confident in the new jet after the October 2018 crash.
Southwest, American Airlines, Tui, and Norwegian have all warned of hits to their profits after the Boeing 737 Max was grounded.
Dennis Muilenburg wrote to Ethiopian Airlines and the airline industry to say Boeing had "thought about the lives lost" in two deadly 737 Max crashes.
Other reports have described the pilot's final moments, which are said to have been spent working through a technical manual in search of a solution.
"Garuda passengers in Indonesia have lost trust and no longer have the confidence" in the plane, a spokesman told Agence France-Presse.
The investigation into October's Lion Air crash has taken on new significance since the fatal crash of an Ethiopian Airlines 737 Max 8 plane.
The investigation into the Lion Air crash has taken on new significance since the fatal crash of an Ethiopian Airlines 737 Max 8 plane.
Ethiopia's transport minister reportedly told The Wall Street Journal that the black boxes from both crashes showed similar data.
