You can use imap to have the client send mail and save it to the server's outbox. So even different mail clients can see the emails in the Sent and Inbox, and even sync them whether they've been read or not.
In my case, my company email supports imap so other clients can see the inbox and sent items.
Office 2008 for Mac was also disappointing in terms of performance and speed compared to Office 2007 on Windows, so I decided to just use Apple Mail. However, in Apple Mail, after sending the mail, the sent letter was not saved on the server. So, when sending mail, we used in-storage.
I've been looking for a way to save a letter from Apple Mail to an imap server for a while and I finally found it.
In Apple Mail, select sent under the inbox and select Mailbox - Use Mailbox as - in the menu, then sent disappears and a folder of email addresses is created under all sent items.
Temporary storage is done in the same way.
It was too simple. All letters sent by this and draft letters are also saved on the server.
Recently, Google's gmail also started to support imap. Therefore, it seems that this method can be used when using gmail as imap in Apple Mail.