552 Message size exceeds maximum permitted

Hi,
This morning I was sending some photographs to a client of mine. I zipped them up and send them through email attachment.
I'm on W7 32bit, NAV2011 v. 18.1.0.37, mailer used: Sylpheed 3.0.3;
Ten minutes afterwards out of the blue NAV 2011 popped up a message on the screen stating this:



Category: Email Errors

Date & Time,
28-10-2010 12:27

Risk
High

Activity
552 Message size exceeds maximum permitted

Status
Error

Recommended Action
No Action Required


The questions/remarks:

1. What is the max. permitted size of an email to be sent before NAV puts its dirty fingers on it?
2. Can this max. permitted size be changed somewhere in NAV?
3. The problem is: I think the message was sent completely and received by the recipient, however why does NAV pop up this message 10 minutes afterwards while already busy doing other tasks?
4. NAV states 'error' : well, if it is an error it was due to NAV2011.
5. NAV  states 'high' risk. A hum, just a couple of RAW picture files with a description in .txt format for the recipient how to handle those. High risk? Yeah, whatever...
6. NAV states as Recommended Action: No Action Required. Well, was the message sent or cut off? You aren't going to tell me I should call the client to ask him/her politely if he/she received the pictures, are you?