I have a number of email accounts and so I would like to be able to view the accounts from which emails were downloaded in the message list. Also, "account" should be available as a matching criterion (in "Condition confguration") when setting up pre-processing/post-processing/filtering rules. I should like to note that both of these features are available in MS Outlook Express.
Explore the fetchinfo plug-in. Using that you can pretty much everything you want except perhaps show a column specifically for this purpose, which I would say is an overkill for this purpose. If I were you, I would use fetchinfo info to set a tag to the message with the account name and then display the tag column. It would essentially do the same thing. This open-ended approach is what makes this software awesome -- no prescribed solutions if possible.
see comment #1, it's already possible.