Server Fault is a question and answer site for system and network administrators. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

A user is experiencing a problem whereby when sending emails, some emails are being allocated the same Message ID. The issue looks to occur when the user has a draft email and they forward the draft to one person, and then later send the draft to another person.

I have done an email trace in Exchange, searching only on Message ID and Exchange is returning the two emails.

Our environment is Outlook 2010 SP1, Exchange 2010 + Exchange 2007, our users run in Outlook Cache Mode.

I have done some research and from what I have read it is the client which generates the Message ID, is this correct?

Is anyone aware of any known issues with two different emails receiving the same Message ID? Does anyone have any knowledge on how this could occur and what we can do to resolve this?

The latest example email's were sent just over 1 hour apart (1 hour, 1 minute), have the same subject, Message ID, sender, but different recipients and message body (only slightly).

share|improve this question
I encountered the same problem sending from Outlook 2010, through Exchange 2010, to multiple Mailman mailing lists with BCC. If a recipient is in more than one mailing list, they will only receive a message from one of the lists, even if there's a multi-hour gap between moderation approvals. – Nic May 12 '13 at 7:19
up vote 3 down vote accepted

There is a history of Message-ID issues with Outlook.

  1. There were reports that Outlook 2003 dispatched e-mails without the Message-ID headers to non-Microsoft MTAs.

  2. There is a feature called Outlook forms that lets one create a template and send messages from a template. All messages have the same message id.

  3. Outlook does not store message-ids of the sent messages.

The problems might be with third-party systems that remove duplicate e-mails from mailboxes, list servers that would not resend a message that they have already seen, systems that trace conversation threads, since there will be multiple messages in a mailbox to link to an 'in-reply-to' reference.

Omitting a message-id altogether is a safer option, since as of the RFC 2822 the existence of a message id is an optional (SHOULD have) requirement, but its uniqueness if it is supplied is necessary (MUST be).

share|improve this answer
The problem we have is that our DMS uses the Message ID to check if the email has already been filed, and because these messages have a duplicate Message ID it is preventing the filing of the messages. We would like to continue the duplicate email check which I guess wouldn't work if the Message ID was ommitted? – Lima May 18 '12 at 3:39
a mail gate such as Exchange or Postfix or anything would assign a message id if a message that comes from outlook lacks one. Mail gate would probably get the messages ahead of the DMS. – Dmitri Chubarov May 18 '12 at 4:20

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.