Allow fallback to configured sender

src/Umbraco.Core/Models/Email/EmailMessage.cs

@@ -33,7 +33,6 @@ namespace Umbraco.Cms.Core.Models.Email
 
         public EmailMessage(string from, string[] to, string[] cc, string[] bcc, string[] replyTo, string subject, string body, bool isBodyHtml, IEnumerable<EmailMessageAttachment> attachments)
         {
-            ArgumentIsNotNullOrEmpty(from, nameof(from));
             ArgumentIsNotNullOrEmpty(to, nameof(to));
             ArgumentIsNotNullOrEmpty(subject, nameof(subject));
             ArgumentIsNotNullOrEmpty(body, nameof(body));

src/Umbraco.Tests.UnitTests/Umbraco.Infrastructure/Extensions/EmailMessageExtensionsTests.cs

@@ -78,5 +78,25 @@ namespace Umbraco.Cms.Tests.UnitTests.Umbraco.Infrastructure.Extensions
             Assert.AreEqual(body, result.TextBody.ToString());
             Assert.AreEqual(1, result.Attachments.Count());
         }
+
+        [Test]
+        public void Can_Construct_MimeMessage_With_ConfiguredSender()
+        {
+            const string to = "to@email.com";
+            const string subject = "Subject";
+            const string body = "<p>Message</p>";
+            const bool isBodyHtml = true;
+            var emailMesasge = new EmailMessage(null, to, subject, body, isBodyHtml);
+
+            var result = emailMesasge.ToMimeMessage(ConfiguredSender);
+
+            Assert.AreEqual(1, result.From.Count());
+            Assert.AreEqual(ConfiguredSender, result.From.First().ToString());
+            Assert.AreEqual(1, result.To.Count());
+            Assert.AreEqual(to, result.To.First().ToString());
+            Assert.AreEqual(subject, result.Subject);
+            Assert.IsNull(result.TextBody);
+            Assert.AreEqual(body, result.HtmlBody.ToString());
+        }
     }
 }