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I have an email address like myname@company1.com and I want to access a shared mailbox sharedmailbox@company2.com, where company1 and company2 are just different names at the same server.

I use Thunderbird/Postbox client instead of Outlook due to important religious matters. And everything works fine if the shared mailbox is @company1.com. I only need to set:

User Name: myname@company1.com\sharedmailbox@company1.com

However, working with company2.com like this:

User Name: myname@company1.com\sharedmailbox@company2.com

does not work at all - the password is not accepted.

How can I work with Exchange's shared mailboxes if the domain names do not match?

Michal Czardybon
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  • Regarding the thought: does not work; I need to provide "myname" somewhere anyway to use my credentials. – Michal Czardybon Jul 01 '16 at 07:57
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    @fixer1234: Some servers have the concept of 'impersonation' (basically sudo but for email), where you always provide _your own_ credentials and the server verifies that you're allowed to access that other mailbox. – u1686_grawity Jul 01 '16 at 08:50
  • @fixer1234: I never said it is an alias... – u1686_grawity Jul 01 '16 at 10:39
  • This is a case where I use my own (myname) credentials to access another mailbox. – Michal Czardybon Jul 01 '16 at 14:33
  • I'll keep an eye on this post for a working answer as **I was never able to get a solution to this between two different domains (not with Thunderbird though) that were setup as two-way trusts**. You can do this all day long with different accounts on the same domain granting appropriate permissions in Exchange to the MB accordingly (full access in my case I believe). Lastly, I was not on Exchange 2016 either so there are some differences in this instance. – Vomit IT - Chunky Mess Style Jul 04 '16 at 05:52

2 Answers2

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As per an answer listed on How to access a Shared Mailbox using Thunderbird or other IMAP client you may just need to define, confirm, or change a unique alias for the shared mailbox in Exchange 2016 and then use the below syntax rather than what you tried per your question.

User Name: myname@company1.com\sharedmailbox (user\shared mailbox alias)

How to access a Shared Mailbox using Thunderbird or other IMAP client

Exchange Configuration

USER EMAIL: user@maindomain.com   
PASSWORD: password
SHARED MAILBOX: shared@anotherdomain.com      (could also be @domain.com, of course)   
SHARED MAILBOX ALIAS: shared-mailbox

Note: Please make sure to create the UNIQUE alias always with the mailbox, because it creates the user [alias]@maindomain.com. In this case shared-mailbox@maindomain.com

Settings for IMAP Configuration

EMAIL ADDRESS: shared@anotherdomain.com (shared mailbox)
IMAP SERVER: outlook.office365.com   
SMTP SERVER: smtp.office365.com
USERNAME: user@maindomain.com\shared-mailbox  (user\shared mailbox alias)   
PASSWORD: password (user's password)

SMTP Login Is Different

USERNAME: user@maindomain.com  (users email)   
PASSWORD: password (user's password)

source

Vomit IT - Chunky Mess Style
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  • This looks like a thing that may work. Still, it feels more like a workaround rather than a solution. Thank you anyway! – Michal Czardybon Jul 12 '16 at 08:41
  • Problem here is that messages are sent as the user not as the shared mailbox. Doesn't work for some user cases. – scotru Nov 10 '16 at 20:04
  • With KDE Kontact I had to set authentication to "NTLM" (or "Clear Text") for this to work as LOGIN/Plain is not supported here. – jayme Apr 05 '17 at 06:46
  • We had to give the incoming user FULL ACCESS rights to the shared email account. This was done within Exchange, not outlook – Otheus Oct 03 '17 at 13:38
1

Just came across this a couple of years later, where the accepted answer did not work for me.

This works with Thunderbird 102.2.2 (IMAP configuration), given that you have permission(*) to access the shared mailbox with your account, say johndoe@example.com:

  • Username: mysharedmailbox@example.com
  • Security: SSL/TLS with OAuth2
    (This is enforced by Microsoft anyway).

Once saved, you'll be prompted with the Microsoft login window. Login as johndoe@example.com with your usual password.

(*) Exchange admin center - (the shared mailbox) - Delegate

jp-jee
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