Implement mail service with configuration and settings management

FoodsharingSiegen.Server/Service/IMailService.cs

@@ -0,0 +1,19 @@
+using System.Threading.Tasks;
+
+namespace FoodsharingSiegen.Server.Service
+{
+    /// <summary>
+    /// Service interface for sending emails.
+    /// </summary>
+    public interface IMailService
+    {
+        /// <summary>
+        /// Sends an email asynchronously.
+        /// </summary>
+        /// <param name="toEmail">The recipient's email address.</param>
+        /// <param name="subject">The subject of the email.</param>
+        /// <param name="htmlBody">The HTML content of the email body.</param>
+        /// <returns>A task that represents the asynchronous email sending operation.</returns>
+        Task SendEmailAsync(string toEmail, string subject, string htmlBody);
+    }
+}