mail-mailer-swallows-blank-line

mail-mailer-swallows-blank-line is a variable defined in `sendmail.el'.
Its value is

nil

• This variable is obsolete since 24.1;
  no need to set this on any modern system.
• This variable may be risky if used as a file-local variable.

Documentation:
Set this non-nil if the system's mailer runs the header and body together.
The actual value should be an expression to evaluate that returns
non-nil if the problem will actually occur.
(As far as we know, this is not an issue on any system still supported
by Emacs.)