Outlook365 supports access via IMAP, POP3 and SMTP protocols. Below you can find the configuration settings for all protocols.

Latest Office 365 version

For latest Office 365 after the service upgrade, use the following settings:

IMAP

Server: outlook.office365.com
SSL: true-implicit, true-explicit (StartTLS)
Port: 993 (default), 143 (default)
User: pat@domain.onmicrosoft.com or pat@your-domain.com

POP3

Server: outlook.office365.com
SSL: true-implicit, true-explicit (StartTLS)
Port: 995 (default), 110 (default)
User: pat@domain.onmicrosoft.com or pat@your-domain.com

SMTP

Server: smtp.office365.com
SSL: true-explicit (StartTLS)
Port: 587(default)
User: pat@domain.onmicrosoft.com or pat@your-domain.com

IMAP and POP3 servers allow both: implicit/TLS SSL and explicit SSL/TLS, so you can ConnectSSL method -or- Connect and StartTLS.

SMTP server requires explicit SSL – use Connect and StartTLS method.

// C#

using (Imap client = new Imap())
{
    client.ConnectSSL("outlook.office365.com");
    client.UseBestLogin("user@domain.onmicrosoft.com", "password");
    ...
}

using (Pop3 client = new Pop3())
{
    client.ConnectSSL("outlook.office365.com");
    client.UseBestLogin("user@domain.onmicrosoft.com", "password");
    ...
}

using (Smtp client = new Smtp ())
{
    client.Connect("smtp.office365.com");
    client.StartTLS();

    client.UseBestLogin("user@domain.onmicrosoft.com", "password");
    ...
}

' VB.NET

Using client As New Imap()
	client.ConnectSSL("outlook.office365.com")
	client.UseBestLogin("user@domain.onmicrosoft.com", "password")
	...
End Using

Using client As New Pop3()
	client.ConnectSSL("outlook.office365.com")		
	client.UseBestLogin("user@domain.onmicrosoft.com", "password")
	...
End Using

Using client As New Smtp()
	client.Connect("smtp.office365.com")
	client.StartTLS()

	client.UseBestLogin("user@domain.onmicrosoft.com", "password")
	...
End Using

Office 365 pre-upgrade

For latest Office 365 pre-upgrade, use the following settings:

On the main screen go to “Options” / “See All Options…”:

Now click the “Settings for POP, IMAP, and SMTP access…” link:

You can find POP, SMTP and IMAP server addresses and settings on the popup window:

Office365 uses default ports for IMAP, POP3 and SMTP protocols. That means that you don’t need to remember port numbers, as Mail.dll .NET email component is going to use correct port numbers by default.

IMAP

Server: podXXXX.outlook.com
SSL: true-implicit
Port: 993 (default)
User: pat@domain.onmicrosoft.com or pat@your-domain.com

POP3

Server: podXXXX.outlook.com
SSL: true-implicit
Port: 995 (default)
User: pat@domain.onmicrosoft.com or pat@your-domain.com

SMTP

Server: podXXXX.outlook.com
SSL: true-explicit
Port: 587 (default)
User: pat@domain.onmicrosoft.com or pat@your-domain.com

IMAP and POP3 servers use implicit SSL – use ConnectSSL method. SMTP server requires explicit SSL – use Connect and StartTLS method.

// C#

using (Imap client = new Imap())
{
    client.ConnectSSL("podXXXX.outlook.com");
    client.UseBestLogin("user@domain.onmicrosoft.com", "password");
    ...
}

using (Pop3 client = new Pop3())
{
    client.ConnectSSL("podXXXX.outlook.com");
    client.UseBestLogin("user@domain.onmicrosoft.com", "password");
    ...
}

using (Smtp client = new Smtp ())
{
    client.Connect("podXXXX.outlook.com");
    client.StartTLS();

    client.UseBestLogin("user@domain.onmicrosoft.com", "password");
    ...
}

' VB.NET

Using client As New Imap()
	client.ConnectSSL("podXXXX.outlook.com")
	client.UseBestLogin("user@domain.onmicrosoft.com", "password")
	...
End Using

Using client As New Pop3()
	client.ConnectSSL("podXXXX.outlook.com")		
	client.UseBestLogin("user@domain.onmicrosoft.com", "password")
	...
End Using

Using client As New Smtp()
	client.Connect("podXXXX.outlook.com")
	client.StartTLS()

	client.UseBestLogin("user@domain.onmicrosoft.com", "password")
	...
End Using

You can find more details about using implicit and explicit SSL or TLS with email protocols:

• Using SSL with IMAP
• Using SSL with POP3
• Using SSL with SMTP

1. Enable IMAP and POP3 protocols

Make sure you have enabled IMAP and POP3. Following articles can help you with that:

• How to enable POP3 in Exchange
• How to enable IMAP in Exchange

2. Turn on basic authentication

Using Exchange Management Console

• Open EMC, expand to Server Configuration->Client Access.
• In the middle panel, click your exchange CAS server, click POP3 and IMAP4 tab, right click IMAP4 and choose properties.
• In Authentication tab, select “Plain text logon (Basic authentication)”, then click OK.
• Open services.msc, restart Microsoft Exchange Transport services.

Using Power Shell

Set-IMAPSettings -Server -LoginType PlainTextLogin
Set-POPSettings -Server -LoginType PlainTextLogin

Open services.msc, restart Microsoft Exchange Transport services.

3. Add permissions to the shared mailbox

Give one user full access permission to the shared mailbox:

Add-MailboxPermission Shared.Mailbox1 -user John.Doe -AccessRights FullAccess

This also can be configured from EMC (Exchange Management Console) gui, by selecting the mailbox and clicking on “Manage Full Access Permission…” at the right pane of the window.

Note: You can not add permissions for user without mailbox, Powershell is the only option in such case.

4. Access the shared mailbox

Exchange 2003

Use the following user format DomainName\Username\SharedMailboxAlias (note the use of SharedMailboxAlias it’s often same as the name but it may be different)
(e.g. DOMAIN\John.Doe\Shared.Mailbox1) to log into the shared mailbox.

Exchange 2007

Install this patch: http://support.microsoft.com/?kbid=949926

Use the following user format DomainName\Username\SharedMailboxAlias (note the use of SharedMailboxAlias it’s often same as the name but it may be different)
(e.g. DOMAIN\John.Doe\Shared.Mailbox1) to log into the shared mailbox.

Exchange 2010, Exchange 2013, Exchange 2016, Exchange 2019

Use the following user format DomainName\Username\SharedMailboxAlias (note the use of SharedMailboxAlias it’s often same as the name but it may be different)
(e.g. DOMAIN\John.Doe\Shared.Mailbox1) to log into the shared mailbox.

Office 365/Exchange Online

Use the following user format Username@DomainName\SharedMailboxAlias

In case of Office 365 SharedMailboxAlias is a local part (no domain and no ‘@’) of the full email address (“Email address” input on “new shared mailbox” screen).

client.Login(@"Username@DomainName\SharedMailboxAlias", "UserPassword");

Using LoginPLAIN to login as a different user

You can try 3rd parameter of LoginPLAIN to log in as a different user:

using (Imap imap = new Imap)
{
    imap.ConnectSSL("outlook.office365.com");

    imap.LoginPLAIN("SharedMailboxAlias", "Username@DomainName", "UserPassword");

    //...

    imap.Close();
}