Doesn't seem to be able to from my testing, but is that a firm fact, it can only email internal USER accounts?
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Can a Nintex workflow send an email to a Shared Mailbox in Exchange Online?
Best answer by cammic
I did find a work around using Nintex Workflow.
1. Created a variable (single line of text) and assigned the AD Mailbox address to this variable, e.g. mech-purchasing@ XXX.edu.au
2. In the Email Action, I used the variable in the TO; field
This seemed to work fine. The emails are appearing in the departments Mail Box.
Still can't use this solution for Flex Task assignments.
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It will only be able to send to users the SharePoint will allow at the moment. So far that is internal user accounts. But how is the shared mailbox configured? does it have an address like something @ internaldomain.com?
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+4I have the same issue. Our Finance team have a group mailbox address MECH-PURCH@XXX.edu.au. When I try an use this email address for Email Notifications or Approvals, it seems to reject it.
How can we assign emails or flex tasks to a MAILBOX rather than an email distribution group or individual email address?
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It does have an @internaldomain.com email address
Tested with distribution groups, shared mailboxes (online in Exchange Online), and mail-enabled security groups. No luck with any of those.
Even SharePoint can email those type of accounts, so not really sure where the hangup is.
I can send emails successfully to mail-enabled security groups IF I add them into a SharePoint Group first.
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+4I did find a work around using Nintex Workflow.
1. Created a variable (single line of text) and assigned the AD Mailbox address to this variable, e.g. mech-purchasing@ XXX.edu.au
2. In the Email Action, I used the variable in the TO; field
This seemed to work fine. The emails are appearing in the departments Mail Box.
Still can't use this solution for Flex Task assignments.
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Can you log into sharepoint with that account and try again? When you say AD mailbox, I assume you created an AD user account.
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+17There is also the possibility to send "External Email" from action, so I guess it is far more easier now.
The solution with a variable often works better than putting email addresses in "TO" field directly. Still dunno why 
Regards,
Tomasz
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+9I ran into this problem and ended up typing in the shared mailbox address in the "external email address" option. It works for now.
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