There are a few different methods for transferring an Outlook OST file to Office 365 or other cloud or webmail email services. Here are some of the most common methods:

1. Convert OST to PST and Import to Office 365:

The first method involves converting the OST file to a PST file format and then importing the PST file into Office 365. Here are the steps to follow:

Step 1: Open Outlook and create a new PST file.

Step 2: Drag and drop the items you want to move from the OST file into the new PST file.

Step 3: Save the PST file to your computer.

Step 4: Sign in to your Office 365 account and go to the Exchange admin center.

Step 5: Create a new import job and select the PST file you saved earlier.

Step 6: Follow the prompts to complete the import.

2. Use a Third-Party Tool:

There are many third-party tools available that can help you transfer your Outlook OST file to Office 365 or another cloud/webmail email service. These tools typically work by converting the OST file to a compatible format and then uploading it to the desired email service. Some popular third-party tools for this purpose include Sysinfo OST to PST Converter, MailConverter OST to PST Converter, and EasyTech OST to PST Migration Tool.

3.  Use an IMAP Account:

Another method involves using an IMAP email account to transfer your Outlook OST file to a new email service. Here are the steps to follow:

Step 1: Create a new IMAP email account with your desired email service.

Step 2: Configure Outlook to connect to the new IMAP account.

Step 3: Drag and drop the items you want to move from the OST file into the new IMAP account.

Step 4: Wait for the items to sync with the new email service.

Step 5: Disconnect the IMAP account from Outlook once the sync is complete.

These are the most common methods for transferring an Outlook OST file to Office 365 or other cloud/webmail email services. Choose the method that works best for you based on your specific needs and preferences.

The best way to manage your OST files is to migrate them into Office 365 account. In this regard, I've recently explored an informative article that discovers the most reliable ways to import Outlook OST to Office 365 account. Here, you will get the complete guide of the manual method and a professional method to perform this migration process with ease.

However, the manual methods are a time-consuming process. Therefore, many experts recommended to opt for an advanced OST to PST converter tool. This tool is easy to use and is capable of migrating bulk OST files to Office 365 accounts without any data loss. It also allows its users to preview their OST file data before starting the migration process. To analyze its performance, try its free demo version. 

The task of importing OST files into Outlook can be very stressful because people regularly doubt the loss of data & damage while importing data. As a result, I endorse using the OST to PST Converter tool this is safe & trustworthy tool & it has a multi-support email platform & gives you a mail filtering option in this option you can transfer OST emails to PST of specific dates email messages & data can be easily managed using this app. Importing OST files into Outlook files is totally free with the free demo. Refer:- https://www.softakensoftware.com/ost-to-pst-converter.html