bug#5558: 23.1.92; sending an email takes much long then previous emacs version

[Glenn Morris]

OK, so it sounds like the issue here was the change of the default
value of `mail-interactive' from nil to t in Emacs 23.1. This should
have been in NEWS but was not (added now).

It means that Emacs will wait for the sendmail process to return and
report any errors, rather than returning immediately and letting
sendmail send a mail in case of error. If it causes unacceptable
delays for you, just set it back to nil.