How to Export Emails from Mimecast (Idiot’s Guide)

How to Export Emails from Mimecast (Idiot’s Guide)

I recently posted an article about an experience a company I know had with Mimecast and their policy on customers exporting data from their own data from their platform.

As a follow up to that, I thought I would post a tutorial to help people who wanted to export their data from the Mimecast platform themselves.  This tutorial covers all the steps from logging in to the Mimecast portal through to exporting data from the platform (as EML files) to reconstructing them as PST files.

Overview of the Mimecast Exporter

The problems with the Mimecast exporter are too numerous to mention here (to my mind I don’t think its too much to ask for a simple ‘export all emails for X user’ option) but the key ones  that we need to address are:

  • You’ll need to know your stubbing threshold (see below)
  • The exporter has a limit of around 500MB of data per export
  • The exporter spits emails out in to individual EML files, combined in to a ZIP file
  • Before you can download any export, it needs to be created as a search first, the run as an export
  • The export process is incredibly slow – I mean we’re talking “run it overnight” slow

Stubbing Threshold

If you are using Mimecast with Microsoft Exchange/Outlook you probably have it setup to push emails to Mimecast that are older than a certain date and leave a stub in Exchange pointing to that messages in Mimecast (the idea being to free up storage space in Exchange).

When you are exporting users’ data from Mimecast , you generally don’t want to export data they already have in their Mailbox so you need to know ‘How long ago’ to export up to – this will be based on the threshold in your Mimecast settings.

Some Quirks to be Aware of

  • Often the button to initiate something, for example ‘Save’ is at the top of the page, before any of the information or options it is an action for – this is far from intuitive (you would expect to progressively work down a form and then have the button to submit/process at the bottom).
  • The year drop down in the Date Selector is awful, it appears to only go back to 2012 – to see further back, you have to select 2012 and then click it again to get the previous years to appear.
  • Some pop up elements such as the Date Selector box may appear below the bottom of the screen, unfortunately when you attempt to scroll down to see them completely, they disappear!  The only solution I found for this was to click the Date Selection (or other popup) and then use either a mouse scroll wheel or a ‘two finger trackpad scroll’ on a laptop to move the page up so I could see the whole thing.
  • For some reason when closing some tabs, the Mimecast portal randomly kicks you out and you have to login again.
  • Sometimes the Date Selector just doesn’t appear when you click it – I found that scrolling to the top of the page and back down solved this (I suspect its because the portal uses multiple nested iFrames – pretty nasty coding).

Stage 1: Exporting Emails

The first step is getting the emails out of Mimecast, this is actually more of an administrative challenge than a technical one because of the 500MB limit per download – each export has to be done in a series of ’rounds’, waiting a day for each export to be prepared.  In addition to this, Inbound messages and Outbound messages needed to be exported separately.

Step 1: Login to the Portal

Go to the Mimecast website at

Click the Login icon in the top-right corner:

You should be presented with a three tabbed box of login options, select Administration & Monitoring

Next click the Login Into Administration and Monitoring > button:

Now enter the email address for an account with administrator privileges

Once redirected to the next login box, change the middle dropdown to Cloud and then enter the password and login:

Step 2: Setup an Export

The first annoyance in the Mimecast portal is you cannot simply choose export, select a user and then hit export.

You have to perform an Archive Search and use the results of that search to initiate the preparation of an export (then you have to wait a day for that export to be prepared):

Click the Administration menu

Click Archive on the left menu

Click Saved Searches from the right hand options that appear

On the Saved Searches page, you may not see a New Search button, if you do not see one, click the New Folder link in the hierarchy on the left hand side:

Click the New Search option which should now be visible at the top of the page

In the Saved Search Description put a descriptive name for this specific search, I would aim to include the user name, direction (received or sent items) and date range.  An example description of mine is:

John Doe Inbox

Scroll down to the Search Filters and Options section

Now we have two options depending on whether we are retrieving all the archived emails a user received or all the messages they sent (‘Sent Items’):

  1. If you are exporting received emails, in the To Address (or Domain) box, enter the email address of the user whose mailbox you are exporting.
  2. If you are exporting sent emails, in the From Address (or Domain) box, enter the email address of the user whose mailbox you are exporting.

Using the Date Range selector, choose a suitable date range for the export – typically this will be the oldest date available up to the ‘stubbing’ date for your Exchange server (see above).

Scroll back to the very top of the page and click the Search button

In the resulting page, you should see a list of emails, including a summary of the number of messages on the right-hand side:

At the top of the page, press the Save and Exit button

You will be asked “The ‘search text’ field is empty. Are you sure you want to continue?“, click OK

You will now have a saved search you can use to initiate an Export.

If you are not already there, navigate to the Saved Searches page (Administration > Archive > Saved Searches)

Right click on the search we just created and select Export Search:

You will now be prompted to choose your export properties:

In the Export Type box, leave Download Messages in Zipped EML SJF Format selected

in the Download Filename box I would recommend using the same naming convention as for the saved search, so as per my example this would be John Doe Inbox

Click Save at the top of the page

You should now – confusingly – be redirected to another form with no buttons, if you look carefully at the bottom you should see a line that says Export preparation is pending.

Next, return to the beginning and create a saved search for the next user (or this users Sent Items) and repeat.

Step 3: Downloading the Exports

Once you have queued up your email exports for ‘preparation’, you should monitor the Exports page for completed export parts.

Exports that are ready to download have a disk icon on the right hand side:

To continue, click the disk icon for the mailbox you are working on

You will be taken to a different page and a ZIP file will start downloading automatically (if it doesn’t, check your pop-up blocker).

Save the ZIP file in a suitable place (I created a folder per mailbox with two folders in it called Inbox and Sent Items), stay on this page in your browser!

IMPORTANT: Do not move on to the next step until your ZIP file has finished downloading, if you do, the ZIP file will get deleted from the Mimecast server before you’ve finished downloading it, leaving you with a corrupted ZIP.

Once the ZIP file has finished downloading, click the Generate Next Export Block button at the top of the page, this will queue up the next 500MB of this mailbox for processing.

Return to the start of this step and repeat until all the Exports listed show zero in the remaining column.

Stage 2: Getting the Emails Back in to Outlook/Exchange

Whether you use Office 365, on-premise Exchange server or any other email service, the next thing you’ll want to do is get all these emails back in to your Inbox/Sent Items.

Unfortunately as they are EML files, Outlook doesn’t allow us to simply drag them to a folder so we have to do a little messing around:

Unzip all of the files for either inbound or outbound mail (e.g. Inbox or Sent) in to  single folder

Download and Install an EML to MSG converter, I recommend Aid4Mail available as a trial and/or paid version from:


Bob McKay

About Bob McKay

Bob is a Founder of Seguro Ltd, a full time father and husband, part-time tinkerer-with-wires, coder, Muay Thai practitioner, builder and cook. Big fan of equality, tolerance and co-existence.

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5 comments on «How to Export Emails from Mimecast (Idiot’s Guide)»

  1. Barbara says:

    Hi, Robert! Thank you so much for this guide. Not sure why you called your instructions an “Idiot’s Guide” 🙂 as it helped me so. It was really painful to split our data to 500MB chunks (ZIPs), but finally I was able to complete all these steps and now all our messages appear in Microsoft Outlook. I found that the aid4mail a bit expensive and used another tool instead. Here is a link if you interested: All troubles are behind and we may say goodbye to Mimecast now! Thanks once again!

  2. Ralph P says:

    They’ve just changed the Search / Export function today to allow export to PST files. The file size has increased to 10GB in 2GB chunks, which should speed things up considerably (I hope – I’m mid-export, extracting 10 years worth of emails).

    1. Bob McKay says:

      Hi Ralph,

      Great thanks for the update – is there a press release or something you saw this on so I can link to it?

  3. Sam says:

    Hello Bob, thank you very much for detailed guide. I was unable to find the way to export emails into PST files at all, so the Ralph’s suggestion did not work for me, but I found the free eml to pst conversion service here and used it to convert Zipped EML files to the solid files of PST format. Thank’s once again! Mimecast now in a distant memory.

  4. Hi Bob. Thanks for recommending our software! We’ve recently released Aid4Mail Enterprise v5 (, which can convert Mimecast archives without unzipping the EML files. It also provides a feature to reorganize emails by account. And if you want to save each account in its own PST file, it will do that too.

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