Postfix cannot send/receive e-mails with large attachments

[PremF]

I'm now using Postfix with Plesk 9.3 on Linux Redhat el5.

At first, Postfix cannot send/receive any e-mail that contains attachment.
But when I have installed Hotfix from http://kb.odin.com/en/6074,
email with attachment can be sent/received if it's a local email (from/to the same server).

BUT in case it's an email with attachment from remote server, if it's quite large (more than 1-2MB),
it can not be received.

Here is what I see in Maillog:

Feb 18 17:33:25 ls1 before-remote[5224]: check handlers for addr: test@localaccount.com
Feb 18 17:33:25 ls1 before-remote[5224]: Processing handlers...
Feb 18 17:33:25 ls1 before-queue[5223]: check handlers for addr: test@remoteaccount.com
Feb 18 17:33:25 ls1 before-queue[5223]: Processing handlers...
Feb 18 10:33:27 ls1 postfix/smtpd[21288]: timeout after DATA from unknown[127.0.0.1]
Feb 18 10:33:27 ls1 postfix/smtpd[21288]: disconnect from unknown[127.0.0.1]
Feb 18 17:33:27 ls1 before-remote[1782]: Timeout reading data from stream
Feb 18 17:33:27 ls1 before-remote[1782]: Unable to read data from stream
Feb 18 17:33:27 ls1 before-remote[1782]: Some error occured
Feb 18 17:33:27 ls1 postfix/spawn[13413]: warning: command /usr/lib64/plesk-9.0/postfix-queue exit status 255
Feb 18 17:33:30 ls1 postfix/spawn[28841]: warning: /usr/lib64/plesk-9.0/postfix-queue: process id 26938: command time limit exceeded

Please suggest how to fix it.

Thank you.