SMTP Services changing?

[BJZeak]

I have now encountered 2 ISP SMTP Servers that appear to have changed the way Emails containing TO and CC are handled.

Normally, an Email sent with TO and CC headers are sent as one EMAIL ... for some reason these 2 Servers are now splitting up the headers and sending TO as one Email transaction and then Sending CC as another separate Email transaction.

Speaking with the ISP's involved, they aren't willing to even discuss this as an issue?

At issue is one of my clients sends Emails with:
a) TO as the Prime Email address candidate

b) CC's using a GROUP Email address that normally contains the Prime Email Address

These Servers are causing the receipt of DUPLICATE INBOUND EMAILS when:
1) FROM/CC Internal originated Emails are Replied to externally with Reply ALL from these servers > TO/CC

2) New external Emails sent with TO/CC from these Servers

Exchange can normally remove duplicate Address Info when an Inbound Email contains both the TO and CC in the same transaction. However, when the Email is received in separate transactions I am not aware of any way it can determine these separate email transactions are related and therefore Users are receiving anoying duplicate traffic.

Has anyone bumped into this? Any ideas how to resolve this?

 

[Zelandakh]

No, emails are sent separately. To and CC are addresses not headers.
Duplicate inbound emails will only occur if the track duplicates is not available/used by other products. If those addresses are different this can be the issue - I've seen that before. Such as multiple SMTP address on the same mailbox and the email is going to both.

 

[BJZeak]

Sorry perhaps I am using the wrong terminology

When I create an email in UNIX, the SUBJECT, TO and CC are all in the first part of the EMAIL being sent (using sendmail) ... If I send an email through what I consider a normal SMTP provider I get ONE email transaction in response which contains both the TO and CC addresses. If however I send this through one of these two other SMTP servers I get TWO separate email transactions.

Understand the only variable we are changing is the SMTP Outgoing server address ... this points to the SMTP service provider ... and ... they don't deny this is how their server works ... they just aren't open to any discussion on why and or a solution.


UNIX sendmail format is:

sendmail -t < <filename>

Where file is in the form:

<subject> -c "<nth CC address> <1st CC address>" <TO address> <email content>

I call the <SUBJECT> <CC> and <TO> info the email header

My clients EXCHANGE server is smart enough to remove duplicates as long as they are in the same email transaction ... this has not changed for the 15 + years that I have been working with this client

Not sure when this actually started ... it was only noticed recently after a user changed their Service provider.