TeamsBotPersonalMessage.cs

using Microsoft.Bot.Builder;
using Microsoft.Bot.Connector;
using Microsoft.Bot.Connector.Authentication;
using Microsoft.Bot.Schema;
using Microsoft.Bot.Schema.Teams;
using Newtonsoft.Json.Linq;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

namespace Teams.Bot.Conversations
{
    class Program
    {
        public static async Task Main(string[] args)
        {
            //Teams internal id
            string teamInternalId = "19:96391bb270744e218c04dc8f571d3d8b@thread.skype";

            //The Bot Service Url needs to be dynamically stored and fetched from the Team. Recommendation is to store the serviceUrl from the bot Payload and later re-use it to send proactive messages.
            string serviceUrl = "https://smba.trafficmanager.net/emea/";

            //the upn of the user who should recieve the personal message
            string mentionUserPrincipalName = "user@tenant.onmicrosoft.com";

            //Office 365/Azure AD tenant id for the 
            string tenantId = "<tenant-GUID>";

            //From the Bot Channel Registration
            string botClientID = "<client-id>";
            string botClientSecret = "<client-secret>";

            var connectorClient = new ConnectorClient(new Uri(serviceUrl), new MicrosoftAppCredentials(botClientID, botClientSecret));

            var user = await ((Microsoft.Bot.Connector.Conversations)connectorClient.Conversations).GetConversationMemberAsync(mentionUserPrincipalName, teamInternalId, default);


            var personalMessageActivity = MessageFactory.Text($"Personal message from the Bot!");

            var conversationParameters = new ConversationParameters()
            {
                ChannelData = new TeamsChannelData
                {
                    Tenant = new TenantInfo
                    {
                        Id = tenantId,
                    }
                },
                Members = new List<ChannelAccount>() { user }
            };

            var response = await connectorClient.Conversations.CreateConversationAsync(conversationParameters);

            await connectorClient.Conversations.SendToConversationAsync(response.Id, personalMessageActivity);
        }
    }
}