Exchange, Domino, Antivirus and Message Size Limit

Recently some users in one scenario reported an issue with email attachments. Generally most of users were compressing large doc, xls files before sending. If any document which is 15 MB in size, it becomes 8 MB only.

In this scenario, following configurations were set-

  • Mail size filtering in McAfee for Exchange is not enabled.
  • Email scanner is set to disable for Virus Scan on workstations as well.
  • Maximum message size is set to 25 MB in Exchange.

But with above configuration also, mails which are 2 MB or 5 MB in size will get bounce back (in idle scenario).

Because there is another limit which can be set in most of antivirus programs, which identifies the ‘original’ size of the compressed content. In McAfee for Exchange, attachments will be replaced by the following message-

DENIAL OF SERVICE ALERT

A denial of service protection limit was exceeded. The file has been removed.
Context: ‘FileName.xls’
Reason: The data size limit was exceeded
Limit: 10 MB
Ticket Number : 335c-xxxx-91d3-xxxx
See your system administrator for further information.
Copyright 1999-2011 McAfee, Inc. All Rights Reserved. http://www.mcafee.com

Antivirus first extract the compressed content and then scans, and if the uncompressed file is larger than the set limit it will replace the attachment with the above warning message. (In McAfee, warning customization is possible)

Solution (McAfee, GroupShield for Exchange) 

Increase the Maximum Expanded File Size in the GroupShield configuration settings.

  1. Click StartProgramsMcAfeeGroupShield for ExchangeGroupShield for Exchange.
  2. In the left pane, click on Policy Manager then click Master Policy.
  3. Open Scanner Control under Filters.
  4. Click Edit to open Options.
  5. Increase the Maximum expanded file size to the required size, up to a maximum of 2047 MB.
  6. Click Save, then click Apply.

Solution (McAfee, Security for Lotus Domino) 

If the system you have can handle scanning such large attachments and the company policy allows it, then increase the Maximum expanded files size to a more suitable value or set it to “Allow Through” and let the Domino Policy handle the mail size restrictions .

  1. Click StartProgramsMcAfeeSecurity for Lotus DominoConfiguration Manager.
  2. Click Policy Manager.
  3. Click whichever Policy you wish setting to apply to i.e. External Mail or Internal Mail (you may wish to set both).
  4. Click Master Policy.
  5. Under filters, click Scanner control.
  6. Click EDIT to open Options.
  7. Modify and increase the Maximum expanded file size up to Larger Number or “Allow Through”.
  8. Click Save, then Apply.

 

More information is available on McAfee site:

https://kc.mcafee.com/corporate/index?page=content&id=KB66309 &

https://kc.mcafee.com/corporate/index?page=content&id=KB66310

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