You may encounter message too large on default postfix configuration.
You can check your default limit by ‘postconf -d | grep message_size_limit’

The original message was received at Sat, 3 Mar 2007 12:47:00 +0800 (EAT) from [xxx.xxx.xxx]

----- The following addresses had permanent fatal errors ----- <info_AT_walkmen.net>
(reason: 552 Error: message too large)

----- Transcript of session follows ----- ... while talking to mail.walkmen.net.:
>>> DATA
<<< 552 Error: message too large
554 5.0.0 Service unavailable

To extend the mail message size, add the following to the main.cf
message_size_limit = 20480000