This behavior makes it easy to access email message from multiple computers. By default, IMAP4 clients don't remove downloaded messages from the email server. IMAP4 clients are much more flexible and generally offer more features than POP3 clients. POP3 also doesn't support public folder access.

POP3 can't synchronize multiple folders on the email server with multiple folders on the client computer. POP3 client programs download messages to a single folder on the client computer (typically, the Inbox). But, you can typically configure a POP3 client to keep copies of downloaded messages on the server. This behavior makes it difficult to access email on multiple computers, since downloaded messages are stored on the local computer. Understanding the differences between POP3 and IMAP4īy default, POP3 clients remove downloaded messages from the email server. Email programs that use POP3 and IMAP4 rely on SMTP to send messages. POP3 and IMAP4 email programs don't use POP3 and IMAP4 to send messages to the email server. Settings users use to set up POP3 or IMAP4 access to their Exchange Online mailboxesĪfter you enable POP3 and IMAP4 client access, you have to give users the information in the following table so that they can connect their email programs to their Exchange Online mailboxes. The proxy server first looks up the assigned pod server (client access server) and then authenticates against that. The delay results from using a proxy server, which introduces an additional hop for authentication. POP3 and IMAP4 provide access to the basic email features of Exchange Online and allow for offline email access, but don't offer rich email, calendaring, and contact management, or other features that are available when users connect with Outlook, Exchange ActiveSync, Outlook on the web (formerly known as Outlook Web App), or Outlook Voice Access.Įach time a person accesses a POP-based or IMAP-based email program to open his or her Microsoft 365 or Office 365 email, that user will experience a delay of several seconds. For information about features offered by specific POP3 and IMAP4 client programs, see the documentation that's included with each application. The features supported by each email client programs vary.

Users can use any email programs that support POP3 and IMAP4 to connect to Exchange Online (for example, Outlook, Windows Mail, and Mozilla Thunderbird).

Disabling Basic authentication will block legacy protocols, such as POP and IMAP. To protect your Exchange Online tenant from brute force or password spray attacks, your organization will need to Disable Basic authentication in Exchange Online and only use Modern authentication for Outlook in Exchange Online. For more information, see What are security defaults?. If you've enabled security defaults in your organization, POP3 and IMAP4 are automatically disabled in Exchange Online.

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