This would be hazardous to begin with as support for these attachments is usually provided on a legacy basis in mail clients; that is, client A and client B could have a very different opinion on the type of the attachment.

It is also possible to allow certain MIME types to be passed through to the list while rejecting or filtering all others.  For instance,

Attachments= Yes,image,application/*msword

allows only the specified attachment types and rejects everything else. If you don't want to reject messages that contain other types of attachments, but just want to remove all other types of attachments, you add the ",Filter" parameter at the end of the line-- i.e.,

Attachments= Yes,image,application/*msword,Filter

This means, "Allow all image and application/*msword attachments, and strip all other attachments".  Again, note that plain text ("Content-Type: text/plain") is always allowed and does not need to be included in the list of allowed attachment types.  Likewise, HTML text is controlled exclusively by the "Language= NoHTML" keyword setting.  Other text subtypes are, however, controlled by "Attachments=", so they need to be listed if you intend to allow them.

Additionally, should you wish to allow all inline uuencoded files but restrict the list to certain MIME types, you can specify, similar to the above, something like

Attachments= All,image,application/*msword

or

Attachments= All,image,application/*msword,Filter

(In the preceding examples note carefully that "image" by itself is equivalent to "image/*", in other words, when you code "Attachments= image", you are saying that all MIME image sub-types, for example, "image/jpeg", "image/gif", and so forth, are to be accepted.  If only certain sub-types are acceptable, for instance if you want to accept only JPEG graphics and ensure that others don't go through, you must specify the types explicitly e.g. "Attachments= image/jpeg".)

Note carefully that simply coding something like "Attachments= image" will not necessarily allow all image files through. This is highly dependent on the client being used by the poster. For instance, if your client attaches all binary files as "Content-Type= application/octet-stream", regardless of whether a given binary is (for instance) an executable image, a Word file, or a compressed archive, and  you send a JPEG to a list with "Attachments= image" set in the header, it will be rejected since the image does not have a "Content-Type: image" tag.

Text Box: Attachments continued by Pam Delaney

©Copyright

JISCmail 2004

Page 5

JISCmail Training

The JISCmail team will be holding a summer workshop again this year at the Rutherford Appleton Laboratory in Oxfordshire. If you are a new list owner or one who would like to know more about the service, please contact the Helpline.