I believe these are still valid...
Main window, view message window, and send message window
Open Help topics
F1
Select all messages
Control + A
Main window and view message window
Print the selected message
Control + P
Send and receive mail
Control + M
Delete a mail message
Delete or Control + D
Open or post a new message
Control + N
Open the Address Book
Control + Shift + B
Reply to the message author
Control + R
Forward a message
Control + F
Reply to all
Control + Shift + R or Control + G (news only)
Open the Inbox
Control + I
Go to the next message in the list
Control + > (greater than)
or Control + Shift + > (greater than)
Go to the previous message in the list
Control + < (less than)
or Control + Shift + < (less than)
View properties of a selected message
Alt + Enter
Refresh news messages and headers
F5
Go to next unread mail message
Control + U
Go to next unread news thread
Control + Shift + U
Go to folder
Control + Y
Main window
Open the selected message
Control + O or Enter
Mark a message as read
Control + Enter or Control + Q
Move between the Folders list (if on), message list, preview pane, and Contacts list (if on).
Tab
Mark all news messages as read
Control + Shift + A
Go to a newsgroup
Control + W
Expand a news thread (show all responses)
Left Arrow or Plus Sign
Collapse a news thread (hide messages)
Right Arrow or Minus Sign
Go to next unread newsgroup or folder
Control + J
Download news for offline reading
Control + Shift + M
Message window—viewing or sending
Close a message
Escape
Find text
F3
Find a message
Control + Shift + F
Switch among Edit, Source, and Preview tabs
Control + Tab
Message window - sending only
Check names
Control + K or Alt + K
Check spelling
F7
Insert signature
Control + Shift + S
Send (post) a message
Control + Enter or Alt + S