Access shared/delegate mailbox of Office 365
There are 2 ways of accessing a shared mailbox in Office 365: first -using regular IMAP authentication and a second one – using OAuth 2.0.
Shared mailbox – basic authentication
Make sure basic authentication is turned on:
Try authenticating to users’ regular mailbox with his credentials to check if basic authentication works and the user/password is correct:
client.UseBestLogin("AlexW@example.com", "AlexWPassword");
Access the shared mailbox
Use the following user format:
Username@DomainName\Shared@DomainName
You must use Login method:
client.Login(@"AlexW@example.com\invoices@example.com", "AlexWPassword");
-or-
alternatively you may use LoginPlain method:
client.LoginPlain("invoices@example.com", "AlexW@example.com", "AlexWPassword");
Don’t use UseBestLogin for Office365 shared mailboxes and basic authentication.
The reason is Office 365 advertises LOGIN PLAIN as a preferred login method and UseBestLogin chooses to use it. However Office 365 does not recognize Username@DomainName\Shared@DomainName user pattern when using LOGIN PLAIN. For Office 365 to accept a LOGIN PLAIN to a shared mailbox, you need to provide all 3 parameters separately: shared mailbox, user and user password – use LoginPlain to do that.
Shared mailbox – OAuth 2.0
It is much simpler with OAuth. Use any of the available OAuth 2.0 flows:
https://www.limilabs.com/blog/oauth2-password-grant-office365-exchange-imap-pop3-smtp
https://www.limilabs.com/blog/oauth2-office365-exchange-imap-pop3-smtp
When you’ve obtained an access token you simply use it to access shared mailbox:
string accessToken = result.AccessToken;
using (Imap client = new Imap())
{
client.ConnectSSL("outlook.office365.com");
client.LoginOAUTH2("invoices@example.com", accessToken);
client.SelectInbox();
List<long> uids = imap.Search(Flag.Unseen);
foreach (long uid in uids)
{
var eml = imap.GetMessageByUID(uid)
IMail email = new MailBuilder().CreateFromEml();
string subject = email.Subject);
}
client.Close();
}