Understanding MIME Whitelists

The gateway device uses MIME (Multipurpose Internet Mail Extension) types to decide which traffic may bypass antivirus scanning. The MIME whitelist defines a list of MIME types and can contain one or many MIME entries.

A MIME entry is case-insensitive. An empty MIME is an invalid entry and should never appear in the MIME list. If the MIME entry ends with a / character, prefix matching takes place. Otherwise, exact matching occurs.

There are two types of MIME lists used to configure MIME type antivirus scan bypassing:

• mime-whitelist list—This is the comprehensive list for those MIME types that can bypass antivirus scanning.
• exception list—The exception list is a list for excluding some MIME types from the mime-whitelist list. This list is a subset of MIME types found in the mime-whitelist.

  For example, if the mime-whitelist includes the entry,video/ and the exception list includes the entry video/x-shockwave-flash, by using these two lists, you can bypass objects with “video/” MIME type but not bypass “video/x-shockwave-flash” MIME type.

  You should note that there are limits for mime-whitelist entries as follows:

  • The maximum number of MIME items in a MIME list is 50.
  • The maximum length of each MIME entry is restricted to 40 bytes.
  • The maximum length of a MIME list name string is restricted to 40 bytes.

Related Topics

JUNOS Software Feature Support Reference for SRX Series and J Series Devices