Email Client – set up the o365 shared mailbox


Email Client – set up the o365 shared mailbox


we have a shared mailbox [email protected] and would like to configure it in Thunderbird (or any other Mail Client)
fill in username using backslash notation: [email protected]\shared_mailbox_alias

In our company, we have a shared email account: [email protected], multiple people need to have access to it. The shared mailbox is configured in Microsoft 365, this solution has multiple advantages: the same calendar, contacts list and access to shared folders. For a shared mailbox with the size under 50GB one does not need an Office365 license.

How to configure a shared mailbox in Outlook ?

No additional steps are needed. You just need to restart your Outlook and the mailbox will be added automatically (Folder pane).

How to set up a shared mailbox as IMAP

IMAP (Internet Message Access Protocol) – is a modern version of email protocol that can synchronize folders and e-mails in both directions. Every message sent from your Email Client – will also be synced with an IMAP server and shared on every device. We’re going to use IMAP to configure Thunderbird (or any other IMAP Client).

The main difference in configuring a standard IMAP mailbox when compared to a shared IMAP mailbox will be to use a username with a backslash, ex: for the shared mailbox [email protected] – the proper IMAP username will be: [email protected]\support

Microsoft 365 Office Shared mailbox: [email protected]
User’s Email: [email protected]

IMAP configuration
E-mail address: [email protected]
Username: [email protected]\support
Password: the password for user mailbox

SMTP configuration (for sending emails)
Username: [email protected]
Password: the password for user mailbox

Office 365 IMAP Server Settings
Server name:
Port: 993
Encryption method: SSL

Office 365 SMTP Server Settings
Server name:
Port: 587
Encryption method: TLS


Q: When trying to send a message using the shared mailbox I see the following SMTP error: STOREDRV.Submission.Exception:SendAsDeniedException.MapiExceptionSendAsDenied; Failed to process message due to a permanent exception with message Cannot submit message.

A: Microsoft Office365 detected that you’re trying to send an e-mail using your username, but “From email” is different (shared mailbox alias). You can fix this by changing Shared mailboxes settings (Microsoft 365 admin center). Go to: Groups / Shared mailboxes / Manage mailbox permissions – Send on behalf.

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