POP3 protocol only downloads emails from your webmail's Inbox and does not sync emails across multiple devices. Thus, if you wish to access your emails anytime from several devices, you should consider using IMAP instead.

Switching from POP3 to IMAP is easy with the following steps:

1. Make a local backup on your emails
2. Remove your POP3 account
3. Set up your account with IMAP
4. Move old emails to your IMAP account (optional)

Firstly, it is recommended to back up your emails to prevent any email loss during the switch by going through the steps below, or by referring to Microsoft Guide: Export or backup email, contacts, and calendar to an Outlook .pst file

1. On your Outlook, go to File.

2. Then, select Open & Export and Import/Export.

3. Choose Export to a file and click Next.

4. Next, choose Outlook Data File (.pst) and click Next.

5. Select your mail account and make sure to tick the “Include subfolders” option. Then, click Next.

6. You may click Browse to select a location to save the backup file. Then, click Finish.

7. Fill in the password for your email backup file and click OK.

8. Your emails will be saved as a pst file in the selected folder location.

After your emails have been backup, you can proceed to remove the POP3 mail account. Below are the steps involve to remove your account:

1. Go to [File] > [Account Settings] > [Account Settings].

2. Select your mail account and click [Remove].

3. Click on [Yes] to continue.

4. Before you close the POP3 mailboxes, create a new folder under your main folders. For example, add an “Old Inbox” folder under the Inbox. You may create this by right-click on the folder and select [New Folder]. Type in the folder's name in the blank space.

5. Next, move the emails that you wish to be restored to your IMAP account in this new folder. You may select the emails and right-click on them. Then, select [Move] to the new folder (eg Old Inbox)

6. Select [Yes].

7. Here, you can see the new folders (Old Inbox and Old Sent) under the main folders.

You may proceed to add the new IMAP account once you have removed the previous POP3 mail account by referring the link below:

Email Setup Guide: Microsoft Outlook (Secure IMAP)

You may skip this step if you want to keep the old emails from the previous POP3 profile on your device locally.
Follow through the steps below if you want to upload and sync the old emails to the server and make them available across all devices using IMAP.

Before you proceed, please make sure your email quota is sufficient to contain all emails.

1. Select the new folder that you have created in your POP3 account such as “Old Inbox” and “Old Sent”. Then, drag and drop it under the IMAP folder. By doing this, you can separate the folder for new and old backup emails.

2. Repeat the step for all of the folders. After you have finished moving the emails, you may close the POP3 account by right-click on the account and select [Close].

You may expect longer synchronisation time in Microsoft Outlook if you have larger folder's size.