Help Managing Your Mailbox and Reducing Mailbox Size

Maintaining a clean mailbox is essential for optimal email performance and productivity. Large mailboxes can slow down Outlook, make it difficult to find important messages, and may exceed storage quotas. By regularly archiving emails, moving attachments to cloud storage, and reducing overall mailbox size, you can improve system performance, ensure compliance with retention policies, and maintain better organization of your communications.

Why Mailbox Management Matters

A bloated mailbox affects more than just storage space. When your mailbox approaches capacity, Outlook performance degrades, search times increase, and you risk being unable to receive new emails. Large mailboxes also take longer to backup and sync across devices. By keeping your mailbox lean, you'll experience faster load times, quicker searches, and more reliable email delivery. Additionally, moving files to cloud storage like OneDrive or SharePoint enables better collaboration, version control, and access from any device.

Understanding Transitory Emails

Not every message needs to be kept. Many emails are transitory, meaning they have short-term informational value only, with no legal, financial, or historical value to the institution. Once a transitory message has served its purpose, it is safe to delete, and clearing these out is one of the fastest ways to reduce clutter and mailbox size. Common examples include:

  • Emails for scheduling or accepting meetings
  • Automated notifications and system alerts
  • Announcements for social events, such as retirement parties or office gatherings
  • Requests for routine information (for example, "What is the printer name?")
  • External newsletters and subscription emails
  • Preliminary drafts, once a final version exists
  • Routine replies and acknowledgment messages

Rule of thumb: Delete a transitory message as soon as you give or receive a reply, or as soon as you no longer need it for reference.

Best Practices for Mailbox Hygiene

Adopt these habits to maintain a healthy mailbox over time. Delete or archive emails older than your organization's retention requirements. Unsubscribe from newsletters and promotional emails you no longer read. Empty your Deleted Items and Junk Email folders regularly. Save important attachments to cloud storage and delete them from emails. Use folders and rules to automatically organize incoming mail, making it easier to identify what can be archived or deleted.

Please note: Some actions may take some time to complete and mailbox may not be responsive depending on size of action, and doing through bwa.dartmouth.edu rather than the Outlook application is recommended. Actions may also be irreversible. If unsure, please schedule a Mailbox Consultation to discuss with a consultant today!

How to Move Attachments to Cloud Storage

  1. Open the email containing the attachment you want to move.
  2. Right-click on the attachment and select Save As.
  3. Navigate to your OneDrive, SharePoint, or other cloud storage location on your computer.
  4. Click Save to store the file in the cloud.
  5. Once saved, you can delete the attachment from the email by opening the email, right-clicking the attachment, and selecting Remove Attachment.
  6. Alternatively, use the Save to Cloud option if available in your version of Outlook to save directly to OneDrive or SharePoint.

How to Archive Old Emails in Outlook

  1. In Outlook, go to File > Options > Advanced.
  2. Under AutoArchive, click AutoArchive Settings.
  3. Check Run AutoArchive every X days and set your preferred frequency (e.g., 14 days).
  4. Set the age of items to archive (e.g., archive items older than 6 months).
  5. Choose where to move old items by specifying an archive file location.
  6. Click OK to save your settings.
  7. To manually archive, go to File > Info > Cleanup Tools > Archive, select the folders and date range, then click OK.

How to Reduce Mailbox Size Quickly

  1. Click on the File tab in Outlook.
  2. Select Info > Mailbox Cleanup.
  3. Use Find items older than to locate emails from a specific time period.
  4. Use Find items larger than to identify emails with large attachments (e.g., over 1 MB).
  5. Review and delete unnecessary large or old emails.
  6. Click Empty Deleted Items Folder to permanently remove deleted emails.
  7. Select View Mailbox Size to monitor your progress and current storage usage.

The 10-Minute Inbox Purge

You do not need a whole afternoon to make progress. Add a recurring 10-minute block to your calendar dedicated to deleting transitory items, then work through this quick sequence:

  1. Filter by sender to group automated alerts (for example, OnBase), then unsubscribe or delete them in bulk.
  2. Search for terms like meeting accepted, confirmed, or re: meeting to find scheduling threads, then delete them.
  3. Sort by oldest date and delete any unread emails from more than a year ago.
  4. Search for external newsletters you no longer need and bulk delete them.

Creating Rules to Manage Incoming Email

  1. In Outlook, go to Home > Rules > Manage Rules & Alerts.
  2. Click New Rule.
  3. Select a template or start from a blank rule, then click Next.
  4. Choose conditions for the rule (e.g., from specific people, with specific words, older than X days).
  5. Choose actions for the rule (e.g., move to folder, delete, flag for follow-up).
  6. Add any exceptions if needed, then click Next.
  7. Name your rule and click Finish.

Before You Hit Send

The best way to manage email is to create less of it. Before sending a message, ask yourself:

  • Does this need to be an email at all?
  • Could it be shared more efficiently on a collaborative platform like SharePoint, Google Share Drive, Dropbox, Teams, or Slack?
  • Could a quick phone call or in-person conversation replace a long thread?

If you answered yes to any of these, consider skipping the email. Less email created means less email to manage later.

Tips for Maintaining a Clean Mailbox

  • Set a recurring calendar reminder (weekly, monthly, or quarterly) to review and clean your inbox.
  • Use the Focused Inbox feature to prioritize important emails.
  • Apply retention policies to automatically delete emails after a specified period.
  • Store project files and documents in Teams or SharePoint instead of emailing them.
  • Use shared mailboxes or distribution lists for team communications instead of CC'ing everyone.
  • Enable email conversation view to group related messages and delete entire threads at once.
  • Compress attachments before sending to reduce file sizes.
  • Consider an annual office-wide cleanup day to make inbox maintenance a shared habit.

External Resources

See Related Articles to the right for more information.

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