If you are using a mail program on more than one computer (desktop, laptop, or smartphone) you need to pay close attention to this article!
If you are using more than 1 device to retrieve your emails, make sure that none of the devices are set to delete messages from the server immediately. If this is the case you may not receive all of your emails on all of your devices appropriately. Also, only set one computer to delete messages from the server after 30 days and not more than one.
Why is this important and what does it affect? If you never use webmail, the frequency of how quickly your computer removes messages from the server is up to you. The way this works is that when your computer removes messages from the server, you will not be able to login to webmail (option 1) and see those messages. It DOES NOT remove your messages from your computer email program, ever. If your computer is set to delete message immediately you will never see any messages in your inbox when logging into webmail directly. However, if you set your computer to delete messages after 1 month, you would always be able to use webmail and at least see that last 30 days of messages on the server.
*** This is not a setting that is controlled on our end with the server, nor is it something that we can give you much direction on. Due to the fact that every mail program is different, we cannot tell you where it is exactly. What we recommend you do is either contact the software company of the program you're using or get in touch with a computer tech company who can help you.