Messages sorted by your filters will always be sent to the designated folder when a match is made. But if you're surprised by the folder to which some or all of your messages are being sent, one of your filters probably contains an incorrect rule or is in an incorrect order.
Incorrect rules often occur if you combine negative criteria, such as "does not contain", with wildcards and/or other positive criteria, such as "contains" or "begins with".
Please note that an "empty" filter is not actually empty. If you create an empty filter at the top of your list and save it without changing anything, then all of your messages will be sent to your inbox, bypassing any other filters you may have. This is because an empty filter says, "If the From: field contains an empty (null) character, then direct the message to the inbox."
Note: Email that is misdirected to a folder will still show up in the unread message summary on your welcome page, which can help you know it's arrived.
The order of your filters has an enormous effect on how messages are filtered. For best results, put your narrowest filters at the top and your broadest filters at the bottom. Once a message matches a filter, it's delivered to a designated folder and not compared to any further filters.
For example, suppose an important piece of mail is sent from firstname.lastname@example.org to your inbox, and you have two simple filters set up:
If Filter A is above Filter B, the message will be compared to Filter A first. Since it contains company.com in the Sender: field (email@example.com), it will be placed in the Company XYZ folder.
On the other hand, if Filter B is above Filter A, the message sent from firstname.lastname@example.org will be compared with Filter B first. The result will be that the Sender: field matches, so the message will be directed to the name folder and not to the Company XYZ folder.