sendmail: avoid sending mail to wrong addresses

sendmail: avoid sending mail to wrong addresses

If we get an address we cannot parse properly, we currently just strip
the unknown characters and still try to send it. This is considered
harmful as the resulting address may still be valid but different from
what the user originally intended.

Instead, skip sending to an address we cannot fully understand and
print the characters what we have scanned so far. Leading and trailing
whitespace is allowed and silently stripped.

Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>