It’s long been an issue/feature with SharePoint Designer 2013 Workflows (yes, some people still use that today), that you cannot send an e-mail to an external email or a shared mailbox. SharePoint Designer 2013 Workflow can only send emails to organization users and a shared mailbox is not a user. So even if you want to send an email to some internal distributionlist or mailbox, you are not able to do that, using 2013 workflow.
If you try sending an email to an external or shared mailbox you will most likely end up with an error like this: “BadRequest to /_vti_bin/client.svc/sp.utilities.utility.SendEmail”.
So to do it, you have to get your “SharePoint Designer 2013 Workflow” to start a “SharePoint Designer 2010 Workflow”. the SPD2010 Workflows only task is to send that email to the shared mailbox.
SharePoint 2010 Site Workflow
Step 1: Create a SPD 2010 Site Workflow
Step 2: Create 3 Initiation form parameters
|emailbody||Multiple lines of text|
|recipient||Single line of text|
|subject||Single line of text|
Step 3: Create a “Send Email” action
Step 4: Input the parameters in the “To”, “Subject” and “Body” areas of the email
Step 5: Publish it
SharePoint 2013 Workflow
Now, the task is to create or edit your SPD2013 Workflow to start the SPD2010 Workflow with the correct parameters.
Step 1: Define 3 variables for use when starting the 2010 Workflow in the next step
Step 2: Create “Start a Site Workflow” action
Step 3: Select the “send email” workflow from the list
Step 4: Match the 3 parameters with the 3 variables
NOTE: The recipient parametervalue should be type = String.
You should end up with a result that looks like this:
Now, each time your SPD2013 Workflow runs, it will start the SPD2010 Workflow to send out the email. This is, so far, the only way I’ve found that a email to an external email or shared email can be sent from a SharePoint Designer Workflow.