Office365 splits emails

[Tsuyoshi Ryu]

Hi There

We are using Office365 and Email security gateway service of other provider.

The email clients are Outlook2013(Please find attached picture)

When we send an email to multi recipients, In some cases, office365 splits the email to multi(We checked the logs in Email Security Gateway)

So the Email Security Gateway acts as multi emails.

We dont know the specific reason of that,  But in our test, when we Bcc someone, Office365 splits the email. But other than that, we'd like know the possible cases that Office365 splits the emails. 

Please kindly give me advice.

Thank you in advance!

[#2]

Not sure what you exactly referring to, but if you send to multi recpients, it sounds as if Exchange Online is doing exactly what its supposed to. more info required otherwise.

[#3]

We just sent an email to multi recipients(To or Cc) . This is one email.

But, office365 sometimes splits the email into 2 or 3 sessions according to the recipient.(We found in the logs)

We'd like to know the cases that Office365 splits the email.

[#4]

When it needs to? Exchange Online ( and any mail server) will bifurcate a message and send as multiple messages when required. Exchange determines when its the best time to do this.

You can read about some that here:

https://technet.microsoft.com/en-us/library/bb430743(v=exchg.150).aspx

Is it causing you problems? 

[#5]

And really, why would you care about how Exchange Online bifuricates messages? As Andy says, the processing in the transport service contains algorithms that figure out the best time to split messages for delivery to multiple recipients. This happens automatically and Exchange has been doing it for a very long time. I don't think there is different behavior in Exchange Online than you see in on-premises servers, so what is the problem and why is it a problem?

In any case, the transport services does its own thing and you're not going to be able to change it.