Handling Large Attachments with Mac Mail

If you have an e-mail message that exceeds 25 MB, it will prevent the upgrade of your e-mail to Office 365. You can use Mac Mail to find e-mails over 25 MB to delete or save attachments to external storage. The following instructions apply to Mail 5 (OS X Lion) or Mail 6 (OS X Mountain Lion).

  1. Open the Mail program.
  2. Click on the Mail menu and select Preferences.
    Select Preferences under Mail menu
  3. Select the Viewing tab and make sure the option labeled “Use classic layout” is checked.
    Note: You can uncheck the option when you're done deleting and saving e-mails over 25 MB.
    Check to use classic layout under Viewing tab
  4. Typically, e-mails are sorted by the date received, with the most recent at the top. The next few steps, will allow you to sort by size.
    Messages sorted by date received
  5. To show the Size column, right-click the column header bar and select Size.
    Right-click column header and select Size if not checked
  6. The Size column will appear showing the size of each message.
  7. Click the Size header to sort e-mails by size, typically largest to smallest from the top. Once sorted, you may have to scroll to the top to see the largest e-mail sizes.
    Messages sorted by size
  8. Open your large e-mails and save any attachment(s) that need to be saved by right-clicking an attachment and selecting Save Attachment. Next, specify where to save the attachment.
    Right-click an attachment and select Save Attachement
  9. Repeat this process for all e-mails that are 25 MB or greater.
  10. Once all e-mail attachments are saved, select and delete the e-mails that are 25 MB or greater.
    Delete e-mails over 25 MB