Most of the email services we use are either POP or IMAP. You will need to know which type of protocol your email service is using before you can set up your email in Outlook successfully.
If you “delete” a message in a POP email account (such as Gmail) accessed through Outlook, it will disappear immediately and you probably find it in the “Deleted Items Folder”. You can further clean the “Deleted Item Folder” and this will permanently delete the message from your computer and you may never find it back if you have not chosen to keep a copy on the mail server.
If you are deleting something in an IMAP email account, neither is it deleted immediately nor does Outlook move it to the “Deleted Items folder”. Instead, these messages are marked for deletion. Outlook will usually indicate that by graying them out, but you can also make it hide deleted messages. You can click on the message with the right mouse button and choose “Undelete” to erase the marks.
Then what should you do if you want to make the marked messages permanently disppear? You have to “purge” the half-gone emails to actually and permanently delete them from the server (or risk running into performance and possibly storage space problems).
Here are two ways you can go and purge deleted messages in Outlook:
1. To purge messages marked for deletion manually: (preferred)
Select Edit | Purge | Purge Marked Items in All Accounts from the menu. This will purge all deleted messages from all IMAP accounts. Of course, you can also choose to purge in only the current folder or its account.
2. To purge deleted messages automatically:
Though this way you have Outlook purge messages marked for deletion automatically when you leave a folder. Firstly open a folder in the IMAP account you want to set up for automatic purging. Secondly, select “Edit | Purge | Purge Options…” from the menu. Third, make sure “Purge items when switching folders while online” is checked. Finally click OK.
Remember that Outlook only purges automatically while you are online. Deleted messages in folders you closed while offline will be purged the next time you visit and leave the folder while online.
Once purged, both the local message and the copy on the mail server will be permanently deleted. Make sure you have archives or copies of the useful messages to avoid mistakenly deletion.