I'm using a POP3 account and have Outlook configured not to leave a copy on the mail server. However, after I download the messages, they are still kept on the server as well.
Why are they still there and not being deleted?
There are 3 common reasons why this could happen.
Virus scanner integration
If you have a virus scanner installed which integrates itself with Outlook, this often the culprit. Especially when the virus scanner is acting like a mail proxy, Outlook no longer talks directly to the mail server but the virus scanner does. This means that the virus scanner is now also responsible to remove the messages from the server and some simply fail to do so.
The solution is easy; disable/uninstall your virus scanner’s integration component for Outlook as you really do not need it anyway.
For more background information and other reasons why you do not need this type of integration see; Disable virus scanner integration?
Mail server option (Gmail)
As it often happens that people remove the messages from the server by mistake via POP3 and POP3 offers no option to copy them back to the server, some mail servers are configured to leave a copy on the server by default, even when the mail client (Outlook) tells it to delete it from the server. A very popular mail service which does this is Gmail.
In this case the solution would be to log into your mailbox via the web based interface and search if there is indeed such an option.
In Gmail you can find this option in the Forwarding and POP/IMAP section;
- Click on the gear icon in the top right corner next to your name and choose; Mail settings
- Click on; Forwarding and POP/IMAP
- For POP3 set the option “When messages are accessed with POP” to; delete Google Mail’s copy
Outlook 2010 Bug – Multiple POP3 account deliver to same pst
With Outlook 2010, we sometimes see this happen when there are multiple POP3 accounts configured and they are all set to deliver to the same pst-file. This only happens in rare situations though and usually these mail profiles have been upgraded from a previous version of Outlook.
The first solution in this case would be to try it with a new mail profile. In addition, let the POP3 accounts deliver their email to their own pst-file file instead of all to a single one. If the messages are properly deleted now, you can reconfigure your account settings to deliver to the same pst-file again.
This bug often also results in the same messages on the server being downloaded again after you restart Outlook.
This bug has been fixed in a later update, so make sure you have all the latest update for Outlook 2010 applied.
Note: The option to leave a copy on the mail server is enabled by default in Outlook 2010. So when you recreate your mail profile, make sure to disable this option for each account that you configure. See: Leave messages on mail server