more lines than relevant to the discussion

Being threading never really caught on in email clients, having the previous emails there for a while is important. At the office, if not for the history, i would have no idea what half the conversation are talking about. Ridiculous as it may seem, the logos and fonts actually help me follow history more easily. It's big, it's gaudy, but it's also an excellent visual cue.

FWIW, gmail has threading with a decent implementation. As a nice touch, the earlier conversation is collapsed, and forwarding entire conversation becomes really easy.

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Added disclaimer. :)