When sending emails with cc copy recipients, header does not show the cc copy email adds it was sent, but, messages are received by all. whats wrong?

Question

Our office email add experiencing this problem just the other day. Our email hosting provider havent found the solution yet despite my frequent follow ups.
Our business partners in Malaysia are already complaining because, suddenly email heading formats changed. Emails they receive from us (we are using the orange outlook express and mozilla thunderbird) when received by them, doesnt show the Cc addresses to whom we sent the email to. But, it is confirmed being received by all, their email adds appearing only in "To:". They are now confused, thinking that we are not cc copying all concerned parties in our emails but in fact we are. We have done test messages and still same problem exists. Hope anyone could help. Thanks in advance!

Answer 1

Confirm your headers are correct:
when you view a 'Sent' email in Sent folder
It shows headers TO and CC with email addresses
When you click on 'Other Actions' and select 'View source'
It says something like this:
'''From - date here'''
X-Mozilla-Status: 0001
X-Mozilla-Status2: 00800000
X-Mozilla-Keys:
Message-ID: info
'''Date: date here'''
'''From: sending email address'''
User-Agent:...Thunderbird/31.4.0
MIME-Version: 1.0
'''To: email address'''
'''CC: email address'''
'''Subject: subject title here'''