Using classic Outlook for Windows in business environments
I understand how frustrating it can be when you're unable to find messages you've already sent.
To better understand your issue, could you please help me check a few things?
-Can you see the Sent Items folder in the folder pane on the left?
-Are your sent messages missing only from Sent Items, or can you also not find them when searching in Outlook?
-Are newly sent messages missing, or are older sent messages missing as well?
-If you sign in to Outlook on the web using the same email account, can you see your sent messages there?
-Could you also check whether Outlook is configured to save copies of sent messages? Please go to File > Options > Mail. Under Save messages, verify whether Save copies of messages in the Sent Items folder is checked.
I look forward to your response.