message-send-mail-function

message-send-mail-function is a variable defined in `message.el'.
Its value is

sendmail-query-once

• This variable may be risky if used as a file-local variable.

Documentation:
Function to call to send the current buffer as mail.
The headers should be delimited by a line whose contents match the
variable `mail-header-separator'.

Valid values include `message-send-mail-with-sendmail'
`message-send-mail-with-mh', `message-send-mail-with-qmail',
`message-smtpmail-send-it', `smtpmail-send-it',
`feedmail-send-it' and `message-send-mail-with-mailclient'. The
default is system dependent and determined by the function
`message-send-mail-function'.

See also `send-mail-function'.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 23.2 of Emacs.