Mail delivery duplication 1

[PKSIT]

I was curious as how an email message was duplicated. Once in a while our network will come to a crawl because someone sends out an attachment that is like 20MB.

Exactly where is an email duplicated when someone sends it to distribution lists?

For example: lets say someone sends a 1MB email to two distribution lists (one list containing 50 people and another containing 200 people). will the exchange server do the duplication? meaning it will turn sending a 1MB email into sending 250MB because it sends it out 250 times.

I'm sure someone can easily answer this for me. I just don't know enough about it.

Thanks in advance.

 

[lhuegele]

I think if the distribution list is a local distribution list, then Outlook would be the one replacing the list name with email addresses before sending to the server. If the distribution list is a server distribution list, then I believe it takes place on the server.

Someone please correct me if I'm wrong, but I think that's correct.

Hope it helps.

 

[PKSIT]

its an Active Directory distribution list

i'm referring to where the actual email gets duplicated, to go out to the people ... where in the process of sending mail does the actual email and its attachments get duplicated to go to the email addresses (many outside email addresses not in house people)

thanks

 

[kmcferrin]

That depends on how your environment is set up. If you are sending to a distribution list that is created in AD/Exchange, then it is "expanded" server-side. If you have a single Exchange server, then it is obviously "expanded" on that PC. If you have multiple mail servers then the answer becomes a lot more complicated. You can specify whether a server is an "expansion" server or not, which affects how email sent to a DL is handled in your environment.

In any case, the message and attachment are still only stored once per message store, even if there are 50 recipients to the message within that store.

There are a lot more details on DL expansion here:

http://support.microsoft.com/kb/328791

 

[lhuegele]

I would have to say that this actually happens in the advanced message queue. The system shouldn't actually be creating "duplicates" so to speak. If one person sends an email to multiple people, whether they come from a distribution list or not, there is still only one document created in the store, and that should be in their sent items folder. When the message reaches the queue though, it should be there, and only there that the message delivery is figured out and the email is sent to multiple external people - it's the same physical email just queued up for multiple external people. If it's to be delivered to internal people, well then of course, it is going to be duplicated for each and every mail box in the information store, but if it's just outgoing SMTP messages, there shouldn't be anything but the one "sent" item taking up space in your store.

Hope that helps.

 

[kmcferrin]

If it's to be delivered to internal people, well then of course, it is going to be duplicated for each and every mail box in the information store,

Actually it shouldn't. There will still only be a single copy of the message per store. All of the mailboxes on that store will have a pointer to the message.

For example, say you send an email to 50 people internally, and those people are on two different mail stores (25 on each). There will a single copy of the message on each mail store, and 25 pointers on each store pointing at that store's copy of the message. There won't be 50 copies of the message, because that would be a ridiculous waste of space.

You can read more about single-instance storage here:

http://support.microsoft.com/kb/175481/en-us

 

[PKSIT]

thanks for all the info guys.

I'm talking more about the outgoing network traffic on our T in terms of how the message is sent to all those external users. if it was going to 50 external users would the message be sent out 50 times? So the outgoing traffic for a 1mb email would be 50mb because it had to be sent out 50 times?

let me know if you need me to clear it up a little.

 

[kmcferrin]

Ah.

Well, if you send an email message to multiple people at the same external company then you only send out a single message. It arrives at the receiving company's MX as a single message with multiple addressees, and gets distributed there.

But if you send out a message to multiple companies then it will make a separate connection and delivery for each MX that it contacts.

The above applies if you are sending a single message to multiple addressees. If you are sending a message, then resending it or sending it again to another group of people it will be treated as a different message altogether.

 

[PKSIT]

thanks kmcferrin, thats exactly what i was looking for.