mutt and gnu utils

[threadul]

in first place sorry for my english.....but I not speak it very
well....

I want obtain the following virtual architecture:
a server: server_A with postfix and dovecot
and severals client with Mutt.

I not want install a MTA in client machines, infact if client1 want
send a mail to client2 I want that this is realised to server_A.

so in this case is necesary an interface between mutt and the smtp
server.
this is possible with mailutils.

I've read a manual that suggest to insert this in Muttrc file:

set sendmail="mail.remote smtp://hostname[:port]"
in my situation it became:
set sendmail="/usr/lib/mailutils/mail.remote smtp://server_A.domain_A:25"
or
set sendmail="/usr/lib/mailutils/mail.remote smtp://192.168.1.1:25"

however when I digit:
mutt -v
I obtain more information and also
SENDMAIL=/usr/sbin/sendmail ...(it is not correct!)

and when I try to send a mail I obtain this error:

Parsing recipient addresses failed: Format of RFC822 object is bad
Error sending message, child exited 1 ().

can you give me some suggest?

the document that i follow is this:
http://gnu.miscellaneousmirror.org/software/anubis/manual/html_section/mail_002eremote.html