Very odd one this. Works perfectly on the Air, but when connected to the external monitor (at a higher resolution) the window goes fully white with the mail information up in the top left and in a VERY small unreadable font. If I close the app and reopen on the Dell monitor (with the Air closed up) the window is completely white with no text at all. The most off thing is that this works occasionally, but other times does the above. Any ideas? Its worth pointing out that this doesn't happen with any other application, be it an Apple one or a third party - just with Thunderbird.