Hi @O'Toole, Anne ,
According to your description, I am afraid it's not feasible to recover those messages back. Given this, it's suggested to check the Drafts folder to
see if you still have any drafts for these emails saved there, otherwise, you would have to recompose the emails from scratch.
The "Clear offline items" option is used to clear offline items in a specific folder, that is, clear the cached items from the OST files as indicated in the prompted dialogue box :
For other folders, we can click the Update Folder button on the Send/Receive tab to recover the items. But items in your Outbox are not synchronized to Exchange server side, so we are not able to undo the "Clear Offline Items" in it.
Furthermore, based on my experience and test, normally messages in Outbox won't be affected by "Clear Offline Items", see the gif below:
However, if the sending message is turned into a "draft" for any reason, it won't be sent as expected and will be removed by "Clear Offline Items":
So next time if you would like to use the Delay delivery feature, aside from making sure Outlook is online and connected, please also confirm the message is not in a "draft" status, this can be determined by checking the icon and the font of a message:
In case a message is already stuck in the Outbox folder, I'd recommend moving a copy to the Drafts folder first as a backup, then you can try removing the delay delivery and click the Send button after opening the message.
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