Sender's email conflict

[dsapikas]

Hello, our infrastructure is for student NGO for research purposes and student exchange network.

In our organisations we have some roles like chair, treasurer etc.
I have been informed today that the treasurer (that uses sentora email) from the one org faced this situation :

He sended an email as treasurer@ngo1.domain.tld but the reply for some reason was send to treasurer@ngo2.domain.tld (this address is not in use yet).

That specific email was send to a private server, not like gmail or hotmail etc.

Do you know what could cause a conflict just like that ?
I am suspecting reverse domain lookup or something like that.
Any workaround suggestions ?



Thank you very much

[apinto]

@[dsapikas]
Theres only one thing capable of causing that (that I know of) and it's the "reply-to" being set to the other email.
I do not believe postfix do it automaticaly (or any other mail service), so please verify if there is a misconfiguration on the client (or webmail).

For example when you setup a account on the Windows Live Mail client (or outlook) you get a screen like:


Anything you put on the "Reply Address" will be the default email the end user gets when they press "Reply" on their end.

UPDATE: Other possibility is that you have some kind of redirect for that email, but that would send EVERY email to the second address and not only replies...

[dsapikas]

That field is empty on the default configuration of RoundCube. I just set the correct one (instead of empty) for that specific user in order to debug any further. Is there any case that that could be caused from any other reason ? Because when i send an email to gmail or outlook etc, i don't face that problem, it just occurred on that case. Receiver's address belongs to a company. So now just for a failsafe we continue the communication through another server. But we don't have any way of debugging that any further. Receiver's address through MX records points at : "vmailin01mx.hol.gr", if that helps by any means.

[apinto]

Can you please post here the contents of the email?
I mean all the "source code" of the email (you can change the IPS and domains for privacy if you wish).

[dsapikas]

MIME-Version: 1.0
Content-Type: multipart/alternative;
boundary="=_2571bce23b54b603e384a56826d152d6"
Date: Tue, 28 Apr 2015 17:31:46 +0300
From: My Name <treasurer@sub1.domain.gr>
To: their-address@domain.tld
Bcc: backupaddr@gmail.com
Subject: Subject
Organization: ORG1
Message-ID: <9bc6cbfab3f662a61781bec2b283298f@esn.teipir.gr>
X-Sender: treasurer@sub1.domain.gr
User-Agent: Roundcube Webmail/1.0.4

--=_2571bce23b54b603e384a56826d152d6
Content-Transfer-Encoding: 8bit
Content-Type: text/plain; charset=UTF-8

blah blah ... (Greeks)

--=_2571bce23b54b603e384a56826d152d6
Content-Transfer-Encoding: quoted-printable
Content-Type: text/html; charset=UTF-8

html blah in Greek

--=_2571bce23b54b603e384a56826d152d6--

[apinto]

I honestly do not see anything weird or wrong.

Is there a probability that the receiver has your contact wrong?
For example, they can have a wrong email address and they might not be hitting "reply", they can be doing "New Mail" and that would cause the error.

If you send that to another company email address (other than the public ones like gmail, yahoo, etc) the same issue happens?

[dsapikas]

To other providers it does not happened [1], and i don't believe that they could by any means have that address because it does not exist.

The only reason i could possible imagine is reverse domain lookup or the Message-ID (?)


[1] - This is why i posted publicly their MX records :?

[apinto]

I can't see how MX or PTR/Reverse DNS records might influence this...
Can you post the email they sent back to you (to the wrong server)?

[dsapikas]

***
From: sender@their.tld
To: treasurer@sub2.domain.tld
CC: supervisor@their.tld
Subject: Subject
Date: Wed, 6 May 2015 10:02:28 +0300
***


I don't have the original mail, because there is no mailbox "treasurer@sub2.domain.tld" on that domain. After some days with no response from them, we just called them and they forwarded it to backupaddr[at]gmail.com

[apinto]

As You can see itnwas clearly sent to the sub2 domain.
I highly suspect it is related to their side.

Is this still happening?