Think you are using Apple Mail at your office. By next month, you are going to be a part of a new organization where you would be using Microsoft Outlook. You must be aware of the fact that email clients don't often use the same file format. For an example: Apple Mail and Microsoft Outlook both are email clients provided by different vendors, ie Apple Mail by Apple Inc. and Outlook by Microsoft Corporation. Though these email clients are used for emailing, but don't share the same file format. Apple Mail stores your mailbox data in MBOX format, while MS Outlook uses PST or personal storage table to store emails and other form of mailbox items. You can't open or access the MBOX files in MS Outlook as it doesn't read such format. In the same way, a PST file can't be opened or accessed in Apple Mail.
If you are switching from one email client to another one, you have to perform email conversion if the file formats supported by the email clients are different. Other than Apple Mail, MBOX file format is supported by various email programs, such as: Thunderbird , Entourage , Spicebird , Netscape , IncrediMail , Claws Mail , PocoMail , Opera Mail , Mozilla Mail , Eudora , Evolution , Sylpheed , Mulberry , SeaMonkey , etc . Apple Mail, Thunderbird, or be it any email client you are using, you have to convert the MBOX files into PST format in order to access your old emails and other mailbox data stored in your MBOX files.
Now the question that comes into one's mind is "how to import MBOX to Outlook". Neither Apple nor Microsoft provides any utility for converting MBOX to PST format. Luckily, there is a manual trick recommended by professionals that may help users import their MBOX files to MS Outlook. Additionally, a 3rd party tool is an alternative solution that can simply convert the MBOX files into PST format. Before switching to a paid converter utility, you must try the manual trick first that doesn't require any cost. Sometimes the manual trick might be time-consuming, even though users can try it once.
There is a major drawback with the manual trick. You have to make sure that your files are valid before you can perform the manual trick. It doesn't work if your MBOX files are corrupt or not in a valid state. In such situation, you need to go to a 3rd party professional converter utility for MBOX to PST conversion. There are plenty of options available over the Internet. Many software companies provide commercialware utilities for converting MBOX files to PST format. Usually such tools are available with trial or demo versions, so that users can download them for free of cost for free evaluation. A proper examination is must before you can purchase any 3rd party tool.