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How to Effectively Increase the Attachment Size Limit in Outlook

Increasing the attachment size limit in Outlook can be a bit complex, as it involves configuring both client-side and server-side settings. Here’s a step-by-step guide to achieve this:

1. Adjusting Attachment Size in Outlook for Desktop

For Outlook 2016, 2019, and Office 365

Note: The following method works for Outlook on Windows.

1. Open the Registry Editor:
   • Press Win + R to open the Run dialog box.
   • Type regedit and press Enter to open the Registry Editor.
2. Navigate to the Registry Key:
   • Go to HKEY_CURRENT_USER\Software\Microsoft\Office\<version>\Outlook\Preferences.
     • Replace <version> with the appropriate version number for your Office installation (e.g., 16.0 for Office 2016, 19.0 for Office 2019).
3. Create or Modify the DWORD Value:
   • In the Preferences folder, right-click on the right pane, select New, and choose DWORD (32-bit) Value.
   • Name it MaximumAttachmentSize.
   • Double-click MaximumAttachmentSize and set the value in KB. For instance, setting it to 102400 will allow attachments up to 100 MB.
4. Restart Outlook:
   • Close and reopen Outlook to apply the changes.

For Outlook 2013 and Earlier

• The same registry modification applies. The steps are similar but the version number in the path will differ (e.g., 15.0 for Outlook 2013).

2. Adjusting Server-Side Limits (For Exchange or Office 365)

If you’re using Exchange Server or Microsoft 365 (Office 365), the server settings may enforce attachment size limits. Here’s how to adjust those settings:

For Exchange Online (Office 365)

1. Log in to Microsoft 365 Admin Center:
   • Go to the Microsoft 365 Admin Center.
2. Access Exchange Admin Center:
   • In the left-hand menu, select Admin centers, then choose Exchange.
3. Modify Message Size Limits:
   • In the Exchange Admin Center, go to mail flow and then rules.
   • Click on the + (plus) sign to create a new rule or modify an existing rule.
   • Adjust the settings under Size to increase the attachment size limit.
4. Adjust Mailbox Settings:
   • Go to recipients, then mailboxes.
   • Select the mailbox you want to adjust, click on the Edit icon, then navigate to Mailbox features.
   • Under Message Size Restrictions, set the desired size limits.

For On-Premises Exchange Server

1. Open Exchange Management Shell:
   • Use the Exchange Management Shell (PowerShell) to modify limits.
2. Run the Command to Set the Limit:
   • Use the following command to set the maximum send and receive size:
   • Set-TransportConfig -MaxSendSize 100MB -MaxReceiveSize 100MB
   • Adjust 100MB to your desired size.
3. Adjust Mailbox Database Limits:
   • For individual mailboxes, use:
   • Set-Mailbox -Identity "MailboxName" -MaxSendSize 100MB -MaxReceiveSize 100MB
   • Replace "MailboxName" with the actual mailbox name.

3. Alternative Solutions for Large Files

If you can’t change the attachment size limits or if they are restricted by the recipient’s email server:

1. Use Cloud Storage:
   • Upload files to OneDrive, Google Drive, Dropbox, etc., and share the link via email.
2. Use File Transfer Services:
   • Services like WeTransfer or SendSpace allow you to send large files without worrying about email attachment limits.

Summary

To increase the attachment size limit in Outlook, you need to:

1. Modify local settings via the Windows Registry for Outlook desktop.
2. Adjust server settings if using Exchange or Office 365.
3. Use alternative methods like cloud storage or file transfer services if needed.

Always ensure that changes comply with your organization’s IT policies and consult with your IT department if necessary.