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Accessing Shared Mailboxes in Office365 with PHP

After a lot of trying&failing, this setup worked for me when connecting to a shared mailbox in office365:

1. As the username, use "your_username\shared_mailbox_alias" (your_username needs access to the shared mailbox of course)
2. Add the extended option 'DISABLE_AUTHENTICATOR' => 'PLAIN'

Example:
$conn = imap_open(
"{outlook.office365.com:993/imap/ssl}Inbox",
'username@domain.com\shared_mailbox_alias',
'mypassword',
OP_READONLY,
1,
array('DISABLE_AUTHENTICATOR' => 'PLAIN')
);