Problem receiving attachments

Hi to everyone,

I've installed a qmail server on a Gentoo linux (2006.1 x86) which, so
far, never produced any strange behaviour.

It's a few days I've got an issue with some emails sent from one of our
providers.

The email sent should have 3 attached files (2 with .txt extension and
one without).

Our email client is Mozilla Thunderbird.

So far, we've always received the email and we were able to see and save
the attached files.
Now, we still receive the email, but the attached files show up like:

begin 600 AZ SCHEDA ART.txt
M"@U/4D]'14P@4RY0+D$N($9)3$E!3$4@1$D@541)3D4@(" @(" @(" @("!-
M3U9)345.5$D@1$D@0T%224-/($4@4T-!4DE#3R @(" @(" @(" @(" @(" @
M(" @(" @(" @(" @(" @(" @(" @(" @(" @(" @(" @(#$R+S$P+S(P,#8*
M#2A-04=!6C S,"D@(" @(" @(" @(" @(" @(" @(" @(" @(" @(" @("!$
M04P@,C4O,#DO,C P-B!!3" S,"\P.2\R,# V(" @(" @(" @(" @(" @(" @
M(" @(" @(" @(" @(" @(" @(" @(" @(" @(" @(" @(%!A9RX@(" @,0H-
M/3T]/3T]/3T]/3T]/3T]/3T]/3T]/3T]/3T]/3T]/3T]/3T]/3T]/3T]/3T]
M/3T]/3T]/3T]/3T]/3T]/3T]/3T]/3T]/3T]/3T]/3T]/3T]/3T]/3T]/3T]
M/3T]/3T]/3T]/3T]/3T]/3T]/3T]/3T]/3T]/3T]/3T]/3T]/3T]/3T]"@T@
M07)T:6-O;&\@(" @(" @(" @(" @(" @(" @(" @(" @(" @(" @1&5S8W)I
M>FEO;F4@(" @(" @(" @(" @(" @(" @(" @(" @(" @(" @(" @(" @(" @
M(" @(" @(" @(" @(" @(" @(" @(" @("!530H-($1A=&$@<F5G+B!#875S
....

They show up UUENCODED!

Here follows the header of the email:

Oggetto: DATI DAL 25/09/06 - 30/09/06.
Da: Filiale di Udine <obfuscated_email_address>
Data:Thu, 12 Oct 2006 10:41:17 +0200
A: <obfuscated_email_address>
Return-Path: <obfuscated_email_address>
Received: from vsmtp19.aaa.bb (xxx.xxx.xxx.xxx) by
ims4a.cp.aaa.bb(xxx.xxx.xxx.xxx) id 451D75E3005534C1 for
<obfuscated_email_address>; Thu, 12 Oct 2006 10:42:55 +0200
Received: from domain.xx (xxx.xxx.xxx.xxx) by
vsmtp19.aaa-bb(xxx.xxx.xxx.xxx) id 452D666C0016F93E for
<obfuscated_email_address>; Thu, 12 Oct 2006 10:42:21 +0200
Received: from www.domain.xx by domain.xx with SMTP
(MDaemon.PRO.v4.0.2.R) for <obfuscated_email_address>; Thu, 12 Oct 2006
10:49:36 +0200
Received: by localhost with Microsoft MAPI; Thu, 12 Oct 2006 10:41:18 +0200
ID-Messaggio: <01C6EDEA.F3537160.xx@domain.xx>
Organizzazione: Organization
X-Mailer: Posta elettronica Internet di Microsoft/MAPI - 8.0.0.4211
Encoding: 4 TEXT, 344 UUENCODE, 150 UUENCODE, 632 UUENCODE
X-MS-Attachment: AZ SCHEDA ART.txt 0 00-00-1980 00:00
X-MS-Attachment: AZDDT.txt 0 00-00-1980 00:00
X-MS-Attachment: RIFATTURA 0 00-00-1980 00:00
X-Return-Path: <obfuscated_email_address>
X-MDaemon-Deliver-To: <obfuscated_email_address>
Content-Type:text/plain

This only happens on some accounts.

Is there anything I could check?

Thanks in advance for your help
Regards,
Carmine