[makecheck]

Personally I've always wanted an E-mail program that would let me edit any message in my mailbox. Why should I be forced to organize my mail according to the poor subject lines that someone else used? And given no subjects at all, I'd be even more interested in having an editing feature.

[a_a_r_o_n]

Thunderbird does that. Message/Edit Message As New.

The intent to send it after editing, but you can just close the message, choose Yes to save to the Drafts folder, and then move it into whatever folder you like. Roundabout but it does what you want.