How does Continuity work in Mimecast for Outlook

Document created by user.oxriBaJeN4 Employee on Sep 16, 2015Last modified by user.oxriBaJeN4 Employee on Dec 29, 2015
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Using a Continuity Event, Mimecast for Outlook can be forced into continuity mode, which is useful if there is a server outage or planned maintenance to the Exchange server.  There are three main phases for the Mimecast for Outlook continuity service:

  • Prior to the Continuity event
  • Delivering messages during the event
  • Ending the Continuity event


Prior to message delivery

The first phase is what happens once a Continuity event is detected, but prior to any messages being retrieved into the end users Inbox. The primary function during this phase is to match messages in the users mailbox with messages in their Mimecast account. This is used to determine if a given message has already been delivered or not, which in turn will ensure that no messages are duplicated in the users mailbox.


During this phase, Mimecast checks all message folders for messages that were delivered prior to the start of the Continuity event. This list is then compared to what the Mimecast believes should have been delivered during that period, and all duplicate emails are reconciled. Mimecast for Outlook then ends up with a list of all undelivered emails which need to be placed into the users mailbox.


Because of some mailbox rules and the way that bulk emails are inserted into the mailbox, there are some cases where duplicate messages are delivered. Unfortunately this cannot be avoided because of the way Outlook places large numbers of emails into non-Inbox folders, but these occurrences should be minimal. Mimecast for Outlook will always err on the side of caution, delivering a message as a duplicate rather than not delivering the message at all.


Delivering Messages during Continuity Event

Once the first phase is complete and relevant messages has been delivered, Mimecast for Outlook begins the task of monitoring Mimecast for new messages, and delivering them to the users Inbox. For the duration of the Continuity event, Mimecast for Outlook will check with the Mimecast Service every minute to see if any new messages have arrived, and these messages are placed in the Inbox.


Mailbox rules that move items out of the Inbox may not work during Mimecast for Outlook continuity. This is because many of these rules are applied by the Exchange server and are therefore not available during a Continuity event. Users will have to manually move these messages during the continuity event if they want them to display in the appropriate folders.

Only emails (IPM.Note) and Calendar items (Outlook 2013 onward) are sent in Continuity mode. Any other file types that are sent during this time will not be delivered until after the event.

During a Continuity event, Mimecast for Outlook monitors the user’s Outbox so that outbound messages can be sent via Mimecast (instead of Exchange). If at the start of an event there are messages in the Outbox, or for any new emails created during the event, Mimecast for Outlook will automatically send these emails via Mimecast.

  • Once the message detail collection process has completed, Mimecast for Outlook starts monitoring the user's Inbox. Any messages found in Mimecast, which were not found during the message details collection stage, will be added to the user's primary Inbox of their mailbox (OST file)
  • Outbound messages will continue to be sent via Mimecast

    Any emails received via Exchange during Continuity mode should be de-duplicated and hard deleted.


Ending the Continuity Event

Once the Continuity event ends, Outlook will once again deliver messages to end users via Exchange. For 10 minutes after the Continuity event has ended, Mimecast for Outlook monitors the incoming messages to ensure that messages that have already been delivered via Mimecast for Outlook during the outage, are not re-delivered.

As with the first phase, messages may arrive in non-Inbox folders. While this isn’t common, duplicate messages may appear in folders outside the Inbox during this phase.


Distribution Lists


Mimecast supports distribution lists during continuity events.  This can be enabled via the option named "Expand Distribution Lists during Continuity Event" when creating or editing an event.


Users who are in an active continuity event will have access to all email sent to any mail enabled group or distribution list they are a member of.  These emails will be available via the Online Inbox of all Mimecast applications (Mimecast for Mobile, Mimecast Personal Portal, Mimecast for Mac and Mimecast for Outlook), including the users local inbox when Mimecast for Outlook is working in continuity mode.


This also applies when viewing the Online Inbox of a delegate mailbox i.e. if the delegate mailbox is in continuity but the other user viewing the mailbox is not, the other user will see mail sent to distribution lists of the delegate.

Active Directory synchronization must be enabled in order for group membership be available.  Group membership is based on the last successful sync.