Navigate in the Finder to the "Mail" app in the "Applications" folder (/Applications/Mail.app), and control-click on its icon. From the resulting contextual menu, select "Show Package Contents"; next, from the resulting Finder window, open the "Contents" folder, and then from the resulting Finder window open the "Resources" folder. The icon that "Mail" uses when new mail arrives is in this folder, with the name "app.icns" (full path is /Applications/Mail.app/Contents/Resources/app.icns). If you replace this file (after saving the original in a safe place of course), with your icon with the same name, "app.icns", your icon should be displayed in the dock under all conditions (no mail/new mail...).
Note that your icon named "app.icns" must be in the ".icns" format... there are at least 2 apps for creating/editing .icns files: IconComposer from the Developer Tools CD, and
Icon Machine III, and maybe someone knows of another?...
I haven't used Icon Machine III, but if you've installed the Developer Tools, IconComposer is very straightforward - only no real editor, and doesn't like to import "Classic" icons; so you'll have to save your icon as an image file (any format) in a graphics editor (Photoshop, etc.).
Then, you can import your icon image (File->Import Image), or drag & drop your images (from the files themselves!)... most image formats, but not Classic icons... into IconComposer; repeat for each icon size, & save the file as "app.icns".
After replacing the file as described above, close the "Mail" folders, and your new icon should appear the next time new mail arrives, or the dock is restarted (not 100% sure on this one, but it will appear with new mail).
BTW, the new mail count red "badge" is also stored in the same folder as above, with the name "newMailBadge1&2.tiff" for 1-2 digit mail counts, & "newMailBadge3.tiff", etc... for more! These can also be replaced with files of the same names... & luckily, these ones are ".tiff" format files. Hope this helps.
acur
[This message has been edited by acur128 (edited 05-24-2001).]