XImages
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What is this ?
It is a new method to distribute images of the author of mail messages for recipients to view.  It has a number of advantages over the People database used by Mail and the XFace header line supported by EnhanceMail and a number of X mailers.

EnhanceMail attaches an X-Image-URL header to outgoing messages.  This header contains a general ftp or http URL pointing to an image.  When EnhanceMail receives a message with such a header, it automatically retrieves the image and displays it.  Furthermore it caches the image persistently so that it doesn't have to be retrieved again.  As the header contains a general URL, it also can be viewed by users of mailers which don't have native support for XImages yet.

Viewing XImages
If you have installed EnhanceMail, attached XImages will automatically be displayed without your having to do anything.  To disable the display of XImages, uncheck the Show XImageURL check box in the Images Preferences panel.  This is recommended for systems which don't have permanent access to the Internet. 

Note that People images from the Mail database will always override XImages, while XImages will override XFaces.

Sending XImages
To send out your own XImage image first a create an image, keeping these points in mind:

·	Mail.app displays images in a 64x64 pixel view.  Images which aren't that size to start with are scaled to that size which for smaller images leads to artifacts and for larger images just wastes disk space and band width.

·	The receiving machine needs to understand the image format.  As GIF, JPG or PNG images require extra software on NeXTs, the recommended format is TIFF.  In any case be sure to give your image a name with the proper extension.

·	If you use the TIFF format, please be kind to the net and LZW compress the image (e.g. with tiffutil).  LZW compression has no impact on image quality and may drastically reduce image size.  JPG compression may or may not reduce the size of the image further, but will make it much harder to display your image for non-NeXT recipients.

·	Most people these days use color displays, so I'd recommend 12 or 24 bit color depth.

Put the image on any publicly accessible ftp or http server.  Then follow these steps.

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Public FTP servers
Some users don't have access to any public ftp or http server.  To help them out the good people at eduStep have offered to make their ftp server available.  Here is a message from them:

eduStep adds EnhanceMail Face archive.

Users of the EnhanceMail 1.2 bundle for NeXTmail 3.3 by Carl Edman <cedman@princeton.edu> need an ftp archive for their mug shots.

If you don't have your own ftp server, the eduStep archive has added a directory for your convenience:

ftp://koala.nmr.embl-heidelberg.de/pub/next/Images/People/

Place your images in:

ftp://koala.nmr.embl-heidelberg.de/pub/next/submissions/
(please give them an unambiguous name, like username.hostname.tiff)

and send a mail to tuparev@EMBL-Heidelberg.de when you have done so.  He'll check that you appear to be who you say you are, and the add/replace your image in the directory.  We're not being paranoid, but you wouldn't want someone maliciously replacing your image with that of Bill Gates, would you?

Caching
EnhanceMail caches all URLs it retrieves for ever in order to save network bandwidth and improve response time.  It will look for cached URLs in the following directories in the given order:

·	 /tmp
·	~/Library/Mail/Images
·	/LocalLibrary/Mail/Images
·	/NextLibrary/Mail/Images

If the image can not be found in any of these directories, it will be retrieved and saved in the last of them which exists and is writable.

Very Important:   Only /tmp exists by default and images saved to /tmp will not survive reboot.  Installers of EnhanceMail are urged in the strongest possible terms to create and make word writable at least one or maybe several of the other directories !

EnhanceMail will also cache failure to retrieve an URL for any reason, including user cancel and inability to access the ftp server.  As long as the cache persists EnhanceMail will not try to retrieve such bad URLs again.

Sysadmins should be free to erase caches at any time.  No harm will come from it except that users may have to retrieve images again.

URLs are only retrieved once.  If they change at a later time, users who retrieved them earlier will not do so again.  So if you change your user image, also change its name.  Whether the old image should be linked to the new one, or remain as is, is a judgement which you have to make.
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