Hi,
In exchange 2010, you can also to the format
DomainName\Username\Alias to log into the shared mailbox. The error "logon failed"
can be caused by the incorrect authentication settings or the IMAP service is stopped. Please follow these steps:
1. Press windows logo key+R to open Run. Type: services.msc. Make sure that Microsoft Exchange IMAP4 service is starting and the startup type is set to "Automatic".
1. Open EMC, expand to Server Configuration->Client Access.
2. In the middle panel, click your exchange
CAS server, click POP3 and IMAP4 tab, right click IMAP4 and choose properties.
3. In Authentication tab, select "Plain test logon (Basic authentication)", then click OK.
4. Open services.msc, restart Microsoft Exchange Transport services.
Please remember to click “Mark as Answer” on the post that helps you, and to click “Unmark as Answer” if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread. Thanks Gen Lin-MSFT