In Outlook 2007 it's only possible to have one Exchange account per Outlook profile. The only way to add another account for an Exchange mailbox is to add it as a POP account.
That being said, we've had to do this for a small number of our customers and it's not pretty. As inconvenient as it may be, my recommendation is to use multiple Outlook profiles, one for each Exchange account.
OK, it looks that I understand what's the problem.
Outlook 2007 takes folder names as case-sensitive, while Cyrus and the rest of the world take them as case-insensitive. So when Outlook asks Cyrus to list the available folders, it gets INBOX.Sent and other INBOX.* folders for a reply. No "Inbox.Sent" among them? Outlook just takes it as the destination folder doesn't exist and doesn't save anything on server. At the same time, it continues to insist there IS "Inbox.Sent" on the server by showing it among IMAP folders! And if you try to tell the server to create "Inbox.Sent" folder, server responds that the folder exists, as Cyrus takes INBOX as case insensitive!
The workaround is to fit the rest of the world to the Microsoft peculiarities by forcibly creating "Inbox.Sent" folder before some other e-mail client creates INBOX.Sent. Then it works with the rest of them, except that you have to specify "Inbox.Sent" explicitly to save the sent messages. And if the client does not allow it (some phone clients), then an extra Sent folder is created.
I've tested it on Apple Mail, Outlook 2003, 2007, 2010, Thunderbird 10.0.2, TheBat! 5.
If anyone has a better idea, please share.
Best Answer
Are they Exchange accounts? As Mathieu has already stated, you can only have one Exchange account per profile.
However, you can open more than one mailbox in a single Exchange profile. Edit the existing Exchange account properties, go into the advanced settings and look for the 'Open these additional mailboxes' section.