Sent messages aren't saved in the Sent Items folder in Outlook 2013

Question

When we send a message in Outlook 2013, a copy of the message should be saved in the Sent Items folder by default. If Outlook doesn’t save a copy of the sent message, it may be caused by any one of the following
reasons:
The “Save copies of messages in the Sent Items folder”
option in Outlook is disabled.
The save location for sent messages was changed to another folder.
There is a custom view set on Sent Items folder, or the view on
Sent Items is corrupt.
Outlook Data File may be damaged.
To resolve the issue, use the appropriate method for your situation.
Enable the Save copies of messages in the Sent Items folder
option
To configure Outlook 2013 to save copies of your sent messages in the Sent Items folder, please follow these steps:
1. Click File tab > Options.
2. Click Mail on the left pane.  
3. Scroll to the Save Messages section, select the check box before “Save copies of messages in the Sent Items folder”.
4. Click OK.
If it is the replying message that is not saving to the Sent Items folder, we need to disable the “When replying to a message that is not in the Inbox, save the reply in the same folder” option in the location mentioned above.
If you’re using an IMAP account, please also make sure you didn’t select the “Do not save copies of sent items” in Account Settings. To check this, Please refer to the following steps:
1. In Outlook, click File tab > Info.
2. Click Account Settings > Account Settings, and then double-click your IMAP account to open the
Change Account wizard.
3. Click More Settings button.
4. Under Sent Items heading, clear the check box before “Do not save copies of sent items”.
5. Click OK and click Next to complete the configuration.
Make sure there is no rule or anything else to redirect sent messages to other folders
To check if it is caused by Outlook rules, please follow these steps:
1. In Outlook 2013, click Home tab.
2. Click Rules > Manage Rules & Alerts.
3. In the rules list, check if there is any rule that applied to the sent messages may cause this issue.
In addition, some rules may be corrupt or hidden and we cannot see them from the rules list. We need to use the MFCMAPI tool to find and delete the corrupt/hidden rules. To do this, we can use the following steps:
1. Download MFCMAPI tool from: http://mfcmapi.codeplex.com/
2. Start MFCMAPI tool.
3. Click Session menu >
Logon, select the Outlook profile you are using and click OK.
4. Double-click the mailbox that contains the inbox rules that you want to delete.
5. A new window will open. In the new window, expand
Root Container or Root – Mailbox, and then expand
Top of Information Store or IPM_SUBTREE.
6. Right click on Inbox and select
Open associated contents table.
7. In the Inbox window, locate and then right-click the items that have the
IPM.Rule.Message message class, and then click Delete Message.
To identify a specific rule, you’ll have to select the rule in the top pane in MFCMAPI and then scroll down in the lower pane and look at the
Property name(s) column. Find the ptagRuleMsgName property name and check the value against the rule name you were trying to delete in Outlook.
8. In the Delete Item dialog, select
DELETE_HARD_DELETE from the Deletion Style drop-down menu.
9. Click OK.
Reset the view settings on Sent Items folder
If you accidently changed the view settings on Sent Items folder, this may cause some sent messages not visible in the folder. To check if you’ve set any view settings on Sent Items folder, please follow:
1. In Outlook, select Sent Items folder.
2. Click View tab from the Ribbon.
3. Click View Settings button. If you notice the
Reset Current View button is clickable, it means the view settings for Sent Items have been changed before.
4. Click the Reset Current View button and then check the Sent Items folder again.
Scan and repair the Outlook Data File
To repair the .pst file, please follow:
1. Find and start the Inbox Repair Tool in the following path:
For Outlook 2013 on a 32-bit version of Windows:
<disk drive>\Program Files\Microsoft Office 15\root\office15
For Outlook 2013 on a 64-bit version of Windows:
<disk drive>\Program Files(x86)\Microsoft Office 15\root\office15
2. In the Inbox Repair tool, click Browse to locate the PST file by using the Windows file system.
3. Click Start.
4. After the analysis scan has completed, it will present you with a scanning report and options for the next step. Click Repair button.
To repair the .ost file, since this type of data file is a copy of information saved on your mail server, we can just delete the OST file and restart Outlook to re-create a new one.
For more information about repair Outlook data files, please refer to this article:
Repair Outlook Data Files (.pst and .ost).
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Answer 1

Same problem here, connecting to a Groupwise (not latest) server. Whenever Mail.app 3 tries to upload/save a new messsage to the server, it would not save and completely lose the message!
I found slightly more information by turning off the "Save to server" option for Sent and Drafts, created a new message that I saved as draft, and then tried to manually move items to the Drafts or Sent folder on the IMAP server.
The error I received was: The message <message> could not be moved to the mailbox <mailbox>-<account>. The IMAP command "APPEND" (to <mailbox>) failed with server error: APPEND NotJunk.
To my inexperienced eyes, it looks like the latest version of Mail changed it's default IMAP handling commands that may be incompatible with older IMAP servers. Anyone else have more insight or know how I can get back Mail.app 2.x from Tiger?