Keep changed app icon after app update?
When you update your OS - (if it contains a Mail.app update) it will replace the previous version of the app with the new one and by doing this it will also replace the icon file.

Anyway something that you can try after you've replaced the icon again:

1.Open Terminal and enter this command - sudo /System/Library/CoreServices/Finder.p/Contents/MacOS/Finder

2.Enter your password and press Enter

3.WITHOUT switching to other windows press CMD + TAB and select Finder

4.Press CMD + N this will open a new Finder Window with root privileges (BE EXTREMELY CAREFUL WHAT YOU DO)

5.Press CMD + G and enter /Applications/Mail.app/Contents/Resources

6.Find the Mail.icns(it should be the new one you chose) file - Right Click it and select Get Info

7.Check the Locked attribute.

8.Go back to the terminal window and press CONTROL + C this will close the Finder Window.

This should prevent it from being overwritten



Command line alternative:

sudo chflags uchg /pathToFile/filename