When you add an email account in a client, such as Outlook, Thunderbird, Apple Mail, Lotus Notes, etc., the client stores a copy of your mail items from the mailbox server to a local data file. Based on the email client you use, the local data file format storing the copy of your mailbox or mail items may vary.
For instance, Outlook creates a separate **OST** or **PST** data file to store mailbox items for each email account you add to the client based on email account type. Similarly, other email clients keep mail items in different file formats. For instance, HCL Notes, Apple Mail, Thunderbird, etc., keep the mail items in **NSF** or **MBOX** files.
If you don’t use an email client but a web browser to access online mailboxes, such as Outlook.com, Yahoo, Gmail, etc., they allow you to export the mailboxes to different file formats. For example, Google allows you to export your Gmail mailbox to MBOX via Google Takeout.
So, in a nutshell, the mailbox data file format may vary based on your email client or the service you use.
However, you can combine the Inbox folders from all your online or offline mailboxes, email accounts, and clients into a single Outlook PST file. This can help you organize emails, create a centralized backup of all your mail items, and access all your Inbox folders or emails from a single Outlook PST file.
**Methods to Merge or Combine Inbox Folders of Multiple Accounts**
When you use Outlook to access multiple email accounts, you see different Inbox folders for each account. You can follow the methods below if you want to merge or combine these Inbox folders of different email accounts into one folder.
In this article, we have shared some manual and automated ways to merge or combine mailboxes and Inbox folders of various email accounts and clients, such as Lotus or HCL Notes, Gmail, Yahoo, Apple Mail, Entourage, Outlook, Office 365, Outlook.com, etc. into a single PST file. You can follow any of the methods based on your requirements. However, for hassle-free process, you can use the advanced mailbox merge utility from Stellar®. [Stellar Merge Mailbox for Outlook](https://www.stellarinfo.com/merge-pst-files-technician.php) can help you merge Inbox folders and other email folders of your online and offline mailboxes in a few clicks.
It’s an [advanced merge mailbox utility to combine multiple mailboxes](https://www.stellarinfo.com/merge-pst-files-technician.php), mail folders, and mail items of all popular email clients and online mailboxes, such as Gmail, Yahoo, Apple Mail, Thunderbird, Outlook.com, Outlook, Office 365, Gmail (MBOX via Google Takeout), Lotus Notes, Entourage, etc. into a single PST file with original folder structure and hierarchy.