Try SYSessential PST to MBOX Converter Software, which can easily export and convert PST to the MBOX file format with a few clicks. You can easily export and convert your selected PST file to email data, including all mailbox items, using this software. The software provides a safe and secure process where even non-technical users can easily export & convert their PST file data into the MBOX file format. This software is also available in a free trial version.
 

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I would like to suggest you useful information about a professional app named PST to MBOX Exporter Online. With the help of this tool, you can definitely convert the PST file to the MBOX Mozilla Thunderbird file. You can save migrated PST files to VCF, EML, MSG, MBOX, HTML, formats. You can indicate any file format to save migrated PST file.

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For export your Outlook information to Thunderbird, Apple Mail or different organizations. This is an entirely dependable instrument that can send out your limitless information at the same time, without making changes and without losing your precious information. It doesn't make a difference how long your documents are. You can send out the vast majority of the documents simultaneously. It's anything but difficult to utilize the device, you can undoubtedly introduce and design PST to MBOX programming with no assistance even, and you can utilize this apparatus autonomously. You don't need to learn tech help to utilize the apparatus. you can also download the free version of this software which exports few items from each folder. you can download this software from here:-https://www.betavare.com/pst/mbox/