message-use-followup-to

message-use-followup-to is a variable defined in `message.el'.
Its value is

ask

Documentation:
*Specifies what to do with Followup-To header.
If nil, always ignore the header. If it is t, use its value, but
query before using the "poster" value. If it is the symbol `ask',
always query the user whether to use the value. If it is the symbol
`use', always use the value.

You can customize this variable.