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

One of the easiest ways to migrate OST files to an Office 365 account is by using a professional OST to PST Converter tool. This is a trustworthy tool that provides a quick migration of OST files with high data accuracy. The Date Range feature helps to convert selective emails of specific dates as per the user's requirements. It also enables bulk migration of OST files to multiple file formats and email clients while keeping the data integrity intact throughout the process.

I have a great solution to import OST files directly into Outlook Office 365 by TrustVare OST to Office 365 Converter Tool which can help you open and import OST files without extending Outlook. Users can import the original OST file in PST and then go directly to Office 365 due to the formats that users expect it to deliver. This application supports MS Outlook 2021, 2019, 2016, 2013, 2010, 2007, and 2003 and uses PST, MSG, EML, EMLX, MBOX etc. For more information, users can avail of its free demo. Users can easily use this tool on Windows 10, 8.1, 8, 7, XP and Vista.

ConverterTools OST to PST Converter tool will be the perfect choice for you to transfer OST email to Office 365 as well as various email clients like Gmail, Yahoo Mail, Hotmail, and many others with their email attachments, for example, email messages, contacts, calendars, tasks, notes, and so on. It also has the great feature of moving OST mailboxes to a number of file formats, like PST, PDF, EML, MSG, MBOX, etc., without losing integrity. You can ignore your duplicate OST emails at the time of the OST conversion process, and it helps to work on all Windows OS versions as well as being highly supported on Mac platforms. Moreover, this tool permits the maintenance of the folder structure according to the actual files and assists in migrating the OST emails to multiple file formats and email clients in a single as well as multiple modes.

MailsDaddy OST to Office 365 Migration Tool is an outstanding solution to recover OST files and migrate them into Office 365 without any hassle. Using this software users can multiple OST files into Office 365 with complete data security. It offers users to open and view the preview of the complete OST file database before migration. Here users can upload single or multiple OST files into one or more O365 accounts at a single time.
It has the ability to transfer OST files into Microsoft 365 Primary and In-Place Archive mailboxes. Users can also transfer heavy OST files into Office 365 without any alteration. This solution can be installed on all Windows systems.
To know more or download the free demo, visit here: OST to Office 365 Migration