Please take a read over this general article on the topic of configuring Sent folders on all of your mail apps and devices. It's important to understand the 'rules' for how this must work before making any configuration changes.
Apple Mail defaults to a sent mailbox/folder named "Sent Messages". If the option to "Store sent messages on the server" is active it will create a folder called "Sent Messages" on the server and use that folder to save copies of sent messages. This conflicts with many other applications which use the folder "Sent" instead.
Here's how to change the default sent mailbox using Apple Mail on macOS 10.12 Sierra:
- Open Mail and choose the "Mail" menu in the upper left. Select Preferences.
- Choose the "Accounts" Tab at the top, then select the account you wish to adjust in the list on the left
- Select the "Mailbox Behaviours" tab on the right
- Under "Sent Mailbox" use the drop down to select the folder called "Sent". Be sure that it is a folder underneath the header indicating your server-side email account and NOT "On My Mac" (that is a local folder). If you do not see such a mailbox, you will need to create it by choosing the Mailbox menu, then selecting New Mailbox. For the Location field, you must select the correct account to create it under (not On My Mac), then set the name to "Sent".
Here's how to change the default sent mailbox for Apple Mail on OS X versions 10.11 and earlier:
- Select the "Sent" folder on the server (in the folders pane on the left) by clicking on it once. It should *not* be at the top of the page next to Inbox/Drafts/Junk/etc, nor should it be under "Local Folders" or "On My Mac". It will be found under a heading indicating that it's a server-side folder. For example, my heading says "Websavers" as it's my Websavers email account.
If you do not see a server-side heading in the folder list or if you do and there is no Sent folder there then you must create a new folder by choosing the Mailbox menu, then "New Mailbox". For the Location field, you must select the correct account to create it under, then set the name to "Sent".
- Chose Mailbox from the system menu at the top of the screen
- Choose "Use this Mailbox as" > and then choose "Sent Mailbox"
Note that if you are unable to select "Sent Mailbox" in step 3 because it is greyed out (disabled), it's because you have not selected a mailbox -- start again, paying close attention to Step 1.
If, after making these changes, you can no longer find your sent emails, look for the old folder called "Sent Messages", then select all messages within and drag and drop them into the new "Sent" folder.