Send emails to authenticated external users using CSOM

Here is some quick code I put together to send emails in SharePoint Online to external users who have accepted sharing invitations and signed in as authenticated users.

Before having look at the code, I should mention my site collection has external sharing turned on and the "Allow external users who accept sharing invitations and sign in as authenticated users" option selected.

And here is the code:

	using Microsoft.SharePoint.Client;
	using Microsoft.SharePoint.Client.Utilities;
	using System;
	using System.Security;
	namespace ExternalUsersEmail
	{
	class Program
	{
	static void Main(string[] args)
	{
	//Authenticated ClientContext. I am using SharePointOnlineCredentials but YMMV.
	var clientContext = GetClientContext();
	var web = clientContext.Web;
	//Full logon name of the authenticated external user you want to send the email to.
	web.EnsureUser("i:0#.f|membership|paige.turner_contoso.com#ext#@tenant.onmicrosoft.com");
	clientContext.ExecuteQuery();
	var emailProperties = new EmailProperties();
	//Email of authenticated external user
	emailProperties.To = new string[] { "paige.turner@contoso.com" };
	emailProperties.Body = "This is the email body";
	emailProperties.Subject = "This is the email subject";
	Utility.SendEmail(clientContext, emailProperties);
	clientContext.ExecuteQuery();
	}
	private static ClientContext GetClientContext()
	{
	string siteUrl = "https://tenant.sharepoint.com/sites/comms/";
	var clientContext = new ClientContext(siteUrl);
	string passwordPlainText = "userpassword";
	string currentUserLoginName = "user@tenant.onmicrosoft.com";
	var passWord = new SecureString();
	foreach (char c in passwordPlainText.ToCharArray()) passWord.AppendChar(c);
	clientContext.Credentials = new SharePointOnlineCredentials(currentUserLoginName, passWord);
	return clientContext;
	}
	}
	}

view raw SendEmailExternalUser.cs hosted with ❤ by GitHub

Thanks for reading!