Invalid characters in yahoo mail

We have application being deploy in development to test send an email in Thai character to customer in internet. This application use production Exchange 2007 SP3 to relay email out.

Recently, I have complain from the application owner saying that when they send a test email to yahoo account, it will show invalid Thai characters. To GMAIL, Hotmail is ok.

I had asked him to a postfix smtp (Unix box) and Exchange 2007 relay (testing environment) to relay email to yahoo, the character show just fine.

The mail flow for:

Exchange Testing env. = Application  > Hub > Edge > Internet

Postfix = Application > PostFix SMTP > Internet

Exchange production = Application > Hub >Edge > Symantec Cloud > Internet.

We suspected Symantec cloud issue, logged a case with them but they found no issue.

Kindly help
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It is likely not an issue of relaying, but the format that is being used to send them, double check the encoding on the outgoing side. there are many possibilities.
i.e. are you using UTF-8 or are you using the specific thai encoding?
Does the Content-type: specify the encoding:?
Content-Type: text/plain; charset=UTF-8

You need to look at the raw message i.e. send one message to three/four addresses, then compare the raw message.

Some might be more tolerant than others.

Yahoo seems to convert to UTF-8 which could explain the issue.
suriyaehnopAuthor Commented:
Here is the content-type:

To: <>
Subject: "Corporate Travel Solutions" Company Registration - Received
MIME-Version: 1.0
Content-Type: multipart/mixed;
X-Mailer: sendHTMLMail
Content-Length: 9357
There is no Content-Type: characterset in the example you posted.
This is what defines the data within.

The contenet-Tyep: multipart/mixed identifies that there are sections i.e. atttachments (inline or attachments) with the boundary used to separate each one.

Each one will have its own Contenet-type: charset=



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suriyaehnopAuthor Commented:
What shall i check further?
Look at the content-type charset in the email on each side.
Check the setting when the email come out raw?
suriyaehnopAuthor Commented:
Here is a internet header at yahoo mail, sent via Exchange Testing Env which the Thai character appear fine.

From Mon Jan 26 08:27:59 2015
X-Apparently-To:; Mon, 26 Jan 2015 08:28:06 +0000
Return-Path: <>
Received-SPF: pass (domain of designates as permitted sender)
X-YMailISG: _aTXhXIWLDu_SREcP6gjnIA1s6r2P25cCIe2cYO2LDkoXkwu
X-Originating-IP: []
Authentication-Results:; domainkeys=neutral (no sig);; dkim=neutral (no sig)
Received: from  (EHLO (
  by with SMTPS; Mon, 26 Jan 2015 08:28:04 +0000
Received: from
( by
( with Microsoft SMTP Server (TLS) id 8.3.389.2; Mon, 26 Jan
2015 16:28:01 +0800
Received: from webx20 ( by
( with Microsoft SMTP Server id 8.3.389.2; Mon, 26 Jan 2015
16:28:00 +0800
Message-ID: <1524066931.1422260879251.JavaMail.root@webappaix20>
Date: Mon, 26 Jan 2015 16:27:59 +0800
From: <>
To: <>
Subject: "Corporate Travel Solutions" Company Registration - Received
MIME-Version: 1.0
Content-Type: multipart/mixed;
X-Mailer: sendHTMLMail
Content-Length: 9392
The point of interest is when each part is individually defined/set.

The header you posted is informative only when looking to determine the path the message took to get to the destination.

Nothing here points to the content other than the content-type that indicates the message has multiple parts.
suriyaehnopAuthor Commented:
Where do i check then..check at the application layer?

Look at the content-type charset in the email on each side.
Check the setting when the email come out raw?

I don't get where to check above? at Exchange ? Application?
the application is the simplest to see whether the output it is transmitting.
Search for the boundary in the header you posted.  Copy the boundary marking and search for it further I. The message.  There you should see another content-type and charset for this section depending on what the content here is. Each again and you will see another ...

What encoding is it using quoted-printables, base64? Does it use UTf-8 for charsetphp/encoding?

When looking in yahoo what is the font that is used versus the font used in the others.?
Unfortunately, I do not know thai, so not sure.

Is there a single invalid character or the entire message is unreadable.  For one determining where it is coming from might be .....
suriyaehnopAuthor Commented:
The entire message was unreadable.
The source email came from same application. If this application user Exchange on ETE/Postfix (unix box), the entire message is fine.
The issue might be with the client, I am not able to tell from what you've posted what is going on.
The user may have their settings such that it is preset with a specific encoding and their settings are such that the application can not correct for the change.

Does it happen to every yahoo recipient?
You have to look at the message headers (raw message where you can see the content-type: of each part of the multi-part attachment).

Unfortunately, if the issue is on yahoo's side, unless the person is paying for their services, he can raise the issue with them and based on their ,.. prioritization it will be looked at.

Not sure whether you are also using HTML to layout the content and whether that is where the issue is.
suriyaehnopAuthor Commented:
Does it happen to every yahoo recipient? try with 2 yahoo account same issue. The issue not happening on GMAIL or hotmail.

Do you know how do i raise the issue with Yahoo?
the recipients can, I do not believe unless they have a specific type of account that it is an issue on their side.

Try the following if you can , a message received on gmail, forward to yahoo.

Is the issue with one specific character/glyph/symbol?
suriyaehnopAuthor Commented:
Please closed this question, problem solved, the issue due to forefront security in ht sever, when i add the sender email address and ip address of the application to trusted sender
suriyaehnopAuthor Commented:
I've requested that this question be closed as follows:

Accepted answer: 0 points for suriyaehnop's comment #a40780495

for the following reason:

I solve the issue
Weren't comments/post I made help focus your search for the culprit?

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suriyaehnopAuthor Commented:
Sine you gave some comment to mt question then i gave you a point
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