Different message size between SMTP and ROUTER

Hi.This is the problem. In console I see:

03/05/2010 09.38.18 SMTP Server: xxxxxxxxxxx.ip.fastwebnet.it (IP xxxxxxxxxxxxxx) connected

03/05/2010 09.38.19 SMTP Server: Message 0029F5D2 (MessageID: <OF507A41CC.95270DAB-ONC1257718.0029BFDB-xxxxxxxxxxxxx>) received from xxxxxxxxxx.ip.fastwebnet.it (IP xxxxxxxxxx) size 147460 bytes

03/05/2010 09.38.19 Router: Message 0029F5D2, 0029BFDB delivered to xxxxxxxxxxxxx/IT from xxxxxxxxxxxxxxxxxxxxx Size: 50K Time: 00:00:00 Hop Count: 1

As you can see, size are very different. And the attachment (PDF, XLS for now) are truncated.

I have reinstalled Domino (8.5.1 FP2 HF34 ita Lang Pack), deleted mail.box, enabled and disabled LZ1, nothing help.

Windows 2003 server with automatic updates.

Frontend SMTP is a Watchguard.

Any idea?