[selowitch]

I know you can create a subfolder and an enclosing folder in Mail.app in one step by choosing Add Mailbox and typing "Family/Cousins" or "Family/Aunts and Uncles". What I can't figure out is how to create a subfolder of the Inbox itself, such that the flippy triangle reveals/hides those subfolders.

Anyone know how?

[El Gato]

I believe subfolders under the Inbox only show up if you have more than one email account set up.

Maybe you can try setting up two accounts for the same email address and using some Rules to direct incoming mail to the folder that you want.

[Diggory Laycock]

You may need to set it up on the server - I think my mailservers allow this via Squirrel Mail.

[edit] - you seem to be able to do it via Mail in the normal way - perhaps your servers admins don't allow creation of new folders.