Sender gets 552 4.3.1 Message size exceeds fixed maximum message size

The mailbox is not full at all. My limit on the mailbox is 30 MB and I am using currently only 3 MB of it

check the message size limit.  Somewhere in exchange, you can set the maximum size of a message can be.

here is where the setting is:

Exchange System Manager > Global Settings > Message Delivery Properties > Default tab)

I am using Exchange 5.5 and the maximum size setting should not have been changed. Email has been working perfectly previously, why would this setting change automatically.

The problem has been fixed now. It was something to do with a new SPAM filter that was setup, that was blocking large attachments.

Thanks for your help guys.

HELP.  I am a student, doing an internship, and the company I'm with has a seemingly unsolvable problem with an Exchange 2000 server.  Other than Global Setting limits of 4,000,000 Kb on sent and received messages, I absolutely cannot find any message size limits set anywhere in the server.  However, no one on our domain is able to receive any messages larger than 2 Mb, yet  we can send any size outgoing just fine.  The company runs ScanMail on the server and after reading the previous comment I looked there, but there are no settings to limit attachment size. Any thoughts?

I forgot to mention, the reason I'm posting under this topic is because those who try to send us large attachments are getting that exact error message, '552 4.3.1 Message size exceeds fixed maximum message size'.  It doesn't matter which of our mailboxes is on the receiving end, or seem to matter where the mail is comming from on the outside, but it's happening to everyone.

if you already checked:
Exchange System Manager > Global Settings > Message Delivery Properties > Default tab)

call tech support for ScanMail.