If you've enabled security defaults in your organization, POP3 and IMAP4 are automatically disabled in Exchange Online. For more information, see Security defaults in Microsoft Entra ID.
Users can use any email programs that support POP3 and IMAP4 to connect to Exchange Online (for example, Outlook, Windows Mail, and Mozilla Thunderbird). The features supported by each email client programs vary. For information about features offered by specific POP3 and IMAP4 client programs, see the documentation that's included with each application.
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.
Note
Each 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. The delay results from using a proxy server, which introduces an additional hop for authentication. The proxy server first looks up the assigned pod server (client access server) and then authenticates against that.
Settings users use to set up POP3 or IMAP4 access to their Exchange Online mailboxes
After 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.
POP3 and IMAP4 email programs don't use POP3 and IMAP4 to send messages to the email server. Email programs that use POP3 and IMAP4 rely on SMTP to send messages.
Protocol
Server name
Port
Encryption method
POP3
Outlook.office365.com
995
SSL/TLS
IMAP4
Outlook.office365.com
993
SSL/TLS
SMTP
Smtp.office365.com
587
STARTTLS
Understanding the differences between POP3 and IMAP4
By default, POP3 clients remove downloaded messages from the email server. This behavior makes it difficult to access email on multiple computers, since downloaded messages are stored on the local computer. But, you can typically configure a POP3 client to keep copies of downloaded messages on the server.
POP3 client programs download messages to a single folder on the client computer (typically, the Inbox). POP3 can't synchronize multiple folders on the email server with multiple folders on the client computer. POP3 also doesn't support public folder access.
IMAP4 clients are much more flexible and generally offer more features than POP3 clients. By default, IMAP4 clients don't remove downloaded messages from the email server. This behavior makes it easy to access email message from multiple computers.
IMAP4 clients support creating and accessing multiple email folders on the email server. For example, most IMAP4 clients can be configured to keep a copy of sent items on the server so these messages are accessible from any computer.
IMAP4 supports additional features that are supported by most IMAP4 clients (for example, viewing message senders and subjects before downloading the entire message).
Send and receive options for POP3 and IMAP4 email programs
POP3 and IMAP4 clients let users choose when they want to connect to the email server to send and receive email. This section discusses some of the most common connectivity options and provides some factors your users should consider when they choose connection options available in their POP3 and IMAP4 email clients.
Common configuration settings
Three of the most common connection settings that can be set on the POP3 or IMAP4 client application are:
To send and receive messages every time the email application is started. When this option is used, mail is sent and received only on starting the email application.
To send and receive messages manually. When this option is used, messages are sent and received only when the user clicks a send-and-receive option in the client user interface.
To send and receive messages every set number of minutes. When this option is used, the client application connects to the server every set number of minutes to send messages and download any new messages.
For information about how to configure these settings for the email application that you use, see the Help documentation that's provided with the email application.
Considerations when selecting send and receive options
The default setting on some email programs is to not keep a copy of messages on the server after they're retrieved. If the user wants to access messages from multiple email programs or devices, they should keep a copy of messages on the server.
For always-connected clients, the user might configure the email application to send and receive messages every set number of minutes. Connecting to the email server at frequent intervals lets the user keep the email application up-to-date with the most current information on the server.
However, if the client isn't always connected to the internet, the user might configure the email application to send and receive messages manually.
Note
If the IMAP4 client supports the IMAP4 IDLE command, email transfers to and from the Exchange Online mailbox might occur in nearly real time.
This article explains how to enable or disable Exchange ActiveSync, MAPI, and Outlook on the web for a mailbox using the EAC or Exchange Online PowerShell.
You use the Set-CASMailbox cmdlet to configure the PO3 and IMAP4 options for each user. The configuration options are described in the following table.
This module examines how clients connect to Microsoft 365. It also provides instruction on how to configure name resolution and Outlook clients, and how to troubleshoot client connectivity.