POP3	IMAP
Emails are downloaded	Emails are synced
Downloaded emails can be left on the server or removed from the server	Emails are left on the server until you delete them
When you delete an email in your mail client, that email may or may not be deleted from the server as well.	When you delete an email in your mail client, that email may be removed from the server, or or may be moved into the deleted items folder on the server.
Sent mail is not stored on the server	Sent mail may or may not be stored on the server
If you've sorted your email into folders, these folders exist on your device, not on the server	Your custom folders may or may not exist on the server

Am I using POP3 or IMAP?

Your mail account could be configured as POP3 or IMAP, and this will determine how you'll need to proceed.

To find out which you're using, you'll need to check your email account settings.

Outlook

In Outlook 2010 or 2013, go to File, then Account Settings. Accounts are on the Email tab.

In Outlook 2016or 2019 click File, then Account Settings and then click the new Account settings option that appears. You'll see a list of your email accounts with Name and Type.

In Outlook 2021 and 365 click select File, then Account Settings and then Manage Profiles. Click Emial accounts

For all versions of Outlook, take note of the Type of your email account, which will be listed as IMAP/SMTP or POP3/SMTP.

Take note of Server Type which will be listed as IMAP Mail Server or POP3 Mail Server.

Open the Mail app, and then click Mail.

Click Settings then click Accounts.

Select your account on the left, and then click the Server Settings tab on the right.

The incoming server will be listed at the top of the Server settings tab like Incoming Server (IMAP) or Incoming Server (POP3).

Open the mail app and click Mail.

Click Preferences, and then click Accounts.

Click the Server Settings tab on the right.

The incoming server will be listed at the top of the Server settings tab like Incoming Server (IMAP) or Incoming Server (POP3).