security woes

i currently have postfix using header_checks to put on hold all emails
being sent with attachments. the reason for this is that i need to
decode base64 in those emails before they can be released. i'm doing
this to check to make sure there isnt any kind of encrypted messages
flowing out of my company. anyway, while a message is on hold, it
gets malformated somehow and the command "perl -MMIME::Base64 -ne
'print decode_base64(print decode_base64($_))' <file" doesnt give me
anything usable. however, once i release the message and run the
exact same command on the mail file, i find what i'm looking for
"AES256 Encrypted File". why would my decode only work once a message
has been released? is there anything i can do to decode it while it's
on hold? any help is greatly appreciated.