Hello.
I have made an applescript for switching through the mailboxes in Mail.app, by the use of a single shortcut key.
ctl-j for next mailbox and ctl-k for previous mailbox. I call the two behaviours up and down, which can be set by a variable so that you can have two instances of the script, one named up and one named down.
The script is supposed to select the first message, which can be really anything depending on how you have sorted that particular mailbox.
This “Highligting” doesn’t always work. The problem is that some messages are threaded. In other scripts I have managed to get the class of the item of the messages of the selected mailboxes to return “Application”.
Then I knew I’d hit the “heading” for a thread and could take action. If somebody could help me with with, so that
messages always becomes hight lighted when I switch to the next mail box I’d be very happy.
The script works pretty good as it is. It is just the finish, I like stuff to work all of the time…
BUGFIX: When a mailbox containing an RSS feed is the selected one it will now jump to the first/last of normal
mailboxes, as it can’t access the RSS account.
This scripts runs under SL, with Mail.app version 4.2
http://macscripter.net/viewtopic.php?pid=128167#p128167 Has a solution, but I can’t seem to get that information out of Mail here. Suggestions are very welcome 
global mboxList, mboxCount, newCurrentMailBox, selMessage, curMailbox, _DOWN, _UP, direction
set mboxList to {}
set selMessage to {}
set newCurrentMailBox to {}
set _DOWN to 1
set _UP to -1
set mboxCount to 0
copy _DOWN to direction
tell application "Mail"
activate
my makeMboxList()
set had to false
try
tell front message viewer
set selMboxCount to count of selected mailboxes
if selMboxCount > 0 then
set selMboxes to selected mailboxes as list
set had to true
end if
end tell
on error
make new message viewer
tell front message viewer
set selMboxCount to count of selected mailboxes
if selMboxCount > 0 then
set selMboxes to selected mailboxes as list
set had to true
end if
end tell
end try
if had = false then
if direction = _DOWN then
set curpos to 1
else
set curpos to mboxCount
end if
copy (item curpos of mboxList) to newCurrentMailBox
my updateMessageViewer(curpos)
else
if selMboxCount > 1 then
if direction = _DOWN then
copy contents of (item mboxCount of selMboxes) to curMailbox
else
copy contents of (item 1 of selMboxes) to curMailbox
end if
try
copy (name of curMailbox) to mboxName -- if mboxName contains "RSS" then error
on error
if direction is _DOWN then
set curMailbox to item -1 of mboxList -- so we jump to the first
else
set curMailbox to item 1 of mboxList -- so we
end if
end try
else -- selMboxCount = 1
set curMailbox to item 1 of selMboxes
try
copy (name of curMailbox) to mboxName -- if mboxName contains "RSS" then error
on error
if direction is _DOWN then
set curMailbox to item -1 of mboxList -- so we jump to the first
else
set curMailbox to item 1 of mboxList -- so we
end if
end try
end if
set curpos to my posInList(curMailbox, mboxList)
if direction = _DOWN then
if curpos = (count of mboxList) then
set curpos to 1
else
set curpos to curpos + 1
end if
else
if curpos = 1 then
set curpos to mboxCount
else
set curpos to curpos - 1
end if
end if
copy item curpos of my mboxList to my newCurrentMailBox
end if
end tell
my updateMessageViewer(curpos)
on makeMboxList()
tell application "Mail"
set tmpList to every mailbox
repeat with aBox in tmpList
set end of my mboxList to contents of aBox
end repeat
set my mboxCount to count of my mboxList
end tell
end makeMboxList
on updateMessageViewer(msgBoxIndex)
local msgCount, sect
set sect to 1
tell application "Mail"
try
tell front message viewer
activate
set msgCount to count of messages of my newCurrentMailBox
repeat until msgCount is not 0
if my direction is my _DOWN and msgBoxIndex is my mboxCount then
set msgBoxIndex to 1
else if my direction is my _UP and msgBoxIndex is 1 then
set msgBoxIndex to my mboxCount
else
set msgBoxIndex to msgBoxIndex + (my direction)
end if
copy item msgBoxIndex of my mboxList to my newCurrentMailBox
set msgCount to (count of messages of my newCurrentMailBox)
end repeat
set selected mailboxes to {my newCurrentMailBox}
if my direction is my _DOWN then
set my selMessage to last message of my newCurrentMailBox
else
set my selMessage to first message of my newCurrentMailBox
end if
set its selected messages to {my selMessage}
end tell
on error e number n
display dialog e
end try
end tell
end updateMessageViewer
on posInList(what, mylist) -- © Matt Neuburg
local ctr
if (count of mylist) = 0 then
return 0
else
set ctr to 1
repeat with anItem in mylist
if contents of anItem is contents of what then
return ctr
else
set ctr to ctr + 1
end if
end repeat
return 0 -- NOT FOUND
end if
end posInList
Best Regards
McUsr
Model: Macbook Pro
AppleScript: 2.1.2
Browser: Safari 533.4
Operating System: Mac OS X (10.6)