Deleting an email by mistake is something most people have done. The good news is that Microsoft 365 gives you more than one chance to recover it before it is permanently gone.
Check the Deleted Items folder first
When you delete an email in Outlook it goes to the Deleted Items folder rather than being permanently removed. Open that folder and look for your email. If it is there, right-click it and select Move, then choose the folder you want to put it back in.
If it is not in Deleted Items
If you have already emptied your Deleted Items folder or cannot find it there, Outlook has a second recovery option called Recover Deleted Items.
In Outlook on your computer, click on the Deleted Items folder in the left panel. In the menu at the top click Folder, then Recover Deleted Items. A window will open showing emails that have been permanently deleted but are still within the recovery window. Select the email you want and click Recover Selected Items.
In Outlook on the web, right-click on Deleted Items in the left panel and select Recover deleted items. The same window will appear.
How long do you have
Microsoft 365 keeps deleted items recoverable for 30 days by default. After that they are gone permanently. If you are looking for something older than 30 days it is very unlikely to be recoverable through standard means.
If you still cannot find it
If the email is genuinely critical and you cannot locate it through either method, it may be worth contacting your IT support. In some cases emails can be recovered through admin-level tools that are not available to regular users. This is something Recloud can assist managed clients with when standard recovery options have been exhausted.