Вот пример работающей отправки письма с аттачем с выключенным NAV

Sanja (v.2) 03.06.2002 17:32

220 beta.kombat.ru ESMTP Sendmail 8.11.6/8.12.1; Mon, 3 Jun 2002 17:30:09 +0400
HELO home
250 beta.kombat.ru Hello d144.p6.col.ru [212.248.5.144], pleased to meet you
MAIL From: <sanja@bougakov.com>
250 2.1.0 <sanja@bougakov.com>... Sender ok
RCPT To: <sanja@bougakov.com>
250 2.1.5 <sanja@bougakov.com>... Recipient ok
DATA
354 Enter mail, end with "." on a line by itself
subject:Test
content-type:multipart/alternative; charset=koi8-r
from:"=?koi8-r?Q?=C0=C0=C0" <sanja@bougakov.com>?=
to:"=?koi8-r?Q?=C1=C1=C1" <sanja@bougakov.com>?=
content-type: multipart/mixed; boundary="lEvEl0"

This is a multi-part message in MIME format.
--lEvEl0

Тест
--lEvEl0
content-type: application/octet-stream
content-disposition: attachment; filename="site.ico"
content-transfer-encoding: x-uuencode

begin 644 site.ico
M```!``$`$!`0``$`!``H`0``%@```"@````0````(`````$`!```````P```
M````````````````````````8_\`.8S_`+W>_P#___\`````````````````
M````````````````````````````````````````````````````````````
M```````````````````````````````````````````S`P`P`P`P`P`S`#`#
M`P`#`S,#,P,P``,````P`S```P`#`#`#`P``,S``,P,`,```````````````
M````````````````````````````````````````````````````````````
M````````````````````````__\``/__``#__P``__\``/__``#__P``__\`
#`/__
`
end

--lEvEl0--
.
250 2.0.0 g53DU9X32407 Message accepted for delivery
QUIT