View source for POP3 vs IMAP

<onlyinclude>
{| class="wikitable"
|+ The most important differences between POP3 and IMAP
|-
! style=width:40em | POP3
! style=width:40em | IMAP

|-

| Emails are '''downloaded'''. 
<ul>
  <li>This means that each email message exists in full as a set of files on your device.</li>
  <li>The email message itself, and all attachments, signatures, etc, ''usually'' exist as separate files on your device.</li>
  <li>'''However''' some mail clients, notably ''Microsoft Outlook'', might handle your email files differently.</li>
</ul>

|| Emails are '''synced'''. 
<ul>
  <li>This means that The files making up each email (the message itself, and all attachments, signatures, etc.) are stored on the server, and your mail client may or may not keep these files on your device as well.</li>
  <li>When you sync your mail, your mail client fetches only the ''headers'' of the mail on the server and displays these to you as a list of the emails in your mailbox.</li>
  <li>The content of an email is ''usually'' only downloaded to your device when you click an email to read it, '''however''' you can change this behaviour with a setting in your mail client.</li>
</ul>

|-

| Downloaded emails can be left on the server '''or''' removed from the server, and this behaviour is controlled by a setting in your mail client.
You can set your mail client to
<ul>
  <li>'''never''' delete mail from the server</li>
  <li>delete email from the server '''as soon as you download it'''</li>
  <li>delete mail from the server '''after a certain number of days'''</li>
  <li>delete email from the server '''when you delete it from your mail client'''</li>
</ul>

|| Emails are left on the server '''at least''' until you delete them from your mail client. 
When you delete an email, the settings in your mail client will determine what happens to that mail on the server:
<ul>
  <li>The email could be deleted from the server right away</li>
  <li>The email could be moved to the <kbd>Deleted items</kbd> or <kbd>Trash</kbd> folder, which:
    <ul>
      <li>can be set to empty when you close your mail client</li>
      <li>can be set to empty periodically every few days</li>
      <li>can be set to never empty automatically. '''This can lead to unexpected storage usage'''</li>
    </ul>
  </li>
</ul>

|-

| 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 exist on your device, and '''may or may not''' exist on the server.

|}
</onlyinclude>
If you're unsure of whether  you're using POP3 or IMAP, you can check the '''account settings''' in your mail client. We've outlined how to do this below. Skip to the section that applies to your mail client:

=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==
<ul>
  <li>
  In Outlook 2010 or 2013
    <ol>
      <li>Click <kbd>File</kbd>.</li>
      <li>Click <kbd>Account Settings</kbd>.</li>
      <li>Click the <kbd>Email</kbd> tab.</li>
    </ol>
  </li>
  <li>
  In Outlook 2016 or 2019
    <ol>
      <li>Click <kbd>File</kbd></li>
      <li>Click <kbd>Account Settings</kbd>.</li>
      <li>Click the new <kbd>Account settings</kbd> option that appears.</li>
    </ol>
  </li>
  <li>
  In Outlook 2021 and 365
    <ol>
      <li>Click <kbd>File<kbd></li>
      <li>Click<kbd>Account Settings<kbd></li>
      <li>Click <kbd>Manage Profiles<kbd></li>
      <li>Click <kbd>Email accounts<kbd></li>
    </ol>
  </li>
</ul>

<mark>For all versions of Outlook</mark>, you'll now see a list of your email accounts with <kbd>Name</kbd> and <mark><kbd>Type</kbd></mark>. Take note of the <kbd>Type</kbd> of your email account, which will be <mark>listed as '''IMAP/SMTP''' or '''POP3/SMTP'''</mark>.

==Thunderbird==
<ol>
  <li>Click on the main <kbd>Menu</kbd> button.</li>
  <li>Go to <kbd>Options</kbd> and select <kbd>Account Settings</kbd>.</li>
  <li>Click <kbd>Server Settings</kbd></li>
  <li> Take note of <kbd>Server Type</kbd> which will be listed as <kbd><mark>IMAP</mark> Mail Server</kbd> or <kbd><mark>POP3</mark> Mail Server</kbd>.</li>
</ol>

==Apple mail==
<ul>
  <li>MacOS 13
    <ol>
      <li>Open the Mail app</li>
      <li>Click <kbd>Mail</kbd></li>
      <li>Click <kbd>Settings</kbd></li>
      <li>Click <kbd>Accounts</kbd></li>
      <li>Select your account on the left</li>
      <li>Click the <kbd>Server Settings</kbd> tab on the right</li>
      <li>The incoming server will be listed at the top of the <kbd>Server settings</kbd> tab like <kbd>Incoming Server (<mark>IMAP<mark>)</kbd> or <kbd>Incoming Server (<mark>POP3</mark>)</kbd></li>
    </ol>
  </li>
  <li>MacOS 12 and earlier
    <ol>
      <li>Open the mail app and click <kbd>Mail</kbd></li>
      <li>Click <kbd>Preferences</kbd></li>
      <li>Click <kbd>Accounts</kbd></li>
      <li>Click the '''Server Settings''' tab on the right</li>
      <li>The incoming server will be listed at the top of the <kbd>Server settings</kbd> tab like <kbd>Incoming Server (<mark>IMAP</mark>)</kbd> or <kbd>Incoming Server (<mark>POP3</mark>)</kbd>
    </ol>
  </li>
</ul>