Long-standing email practice (i.e. pre-dating any Microsoft involvement in email) is to use indents and > symbols to show quote levels. > Fred said >> Dave said >>> Joe said >> > Joe posted something. Dave replied. Fred commented on Dave's reply. The position of Fred's comment would be chosen make it clear that he was commenting on Dave's post and not directly replying to Joe. Thunderbird simply replaces those nested > symbols with coloured bars. This is local and is purely cosmetic. Under the hood, so to speak, the > symbols are still there. People who complain about this usually seem to have been brainwashed by Microsoft's lame attempt at tracking "who said what" by separating succesive posts with horizontal rules. Absolutely useless if you want to answer questions point by point (bottom posting or interleaved posting) rather than the top posting practice that Microsoft customarily assume and encourage. Those same users often resort to using coloured text or other tricks to differentiate later replies from the text of earlier postings. All well and good until the message is viewed in a client or on a device where the colours aren't supported. In such a case, the > symbols would survive and allow the logical flow to be reasoned out. You can switch Thunderbird to using the > symbols rather than converting them to the coloured bars. http://kb.mozillazine.org/Quote_bars But I wonder if you're actually hankering for the default Microsoft-driven top-posting convention?