Open MailKit secure socket option setting

Author: Arthur Chia

src/Serilog.Sinks.Email/Sinks/Email/EmailConnectionInfo.cs

@@ -1,11 +1,11 @@
 // Copyright 2014 Serilog Contributors
-// 
+//
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
-// 
+//
 //     http://www.apache.org/licenses/LICENSE-2.0
-// 
+//
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
@@ -14,6 +14,9 @@
 
 using System.ComponentModel;
 using System.Net;
+#if MAIL_KIT
+using Serilog.Sinks.Email.Sinks.Email;
+#endif
 
 namespace Serilog.Sinks.Email
 {
@@ -80,7 +83,7 @@ public EmailConnectionInfo()
         /// </summary>
         /// <remarks>
         /// This only works on `netstandard1.3` with `MailKit`. If you
-        /// are targeting `net45`+, you should add your validation to 
+        /// are targeting `net45`+, you should add your validation to
         /// `System.Net.ServicePointManager.ServerCertificateValidationCallback`
         /// manually.
         /// </remarks>
@@ -95,5 +98,12 @@ public EmailConnectionInfo()
         /// Sets whether the body contents of the email is HTML. Defaults to false.
         /// </summary>
         public bool IsBodyHtml { get; set; }
+
+#if MAIL_KIT
+        /// <summary>
+        /// Sets secure socket option for MailKit
+        /// </summary>
+        public MailKitSecureSocketOptions? MailKitSecureSocketOption { get; set; }
+#endif
     }
 }

src/Serilog.Sinks.Email/Sinks/Email/MailKitEmailSink.cs

@@ -1,11 +1,11 @@
 // Copyright 2014 Serilog Contributors
-// 
+//
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
-// 
+//
 //     http://www.apache.org/licenses/LICENSE-2.0
-// 
+//
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
@@ -25,6 +25,7 @@
 using Serilog.Sinks.PeriodicBatching;
 using MailKit.Net.Smtp;
 using System.Threading.Tasks;
+using MailKit.Security;
 
 namespace Serilog.Sinks.Email
 {
@@ -61,7 +62,7 @@ public EmailSink(EmailConnectionInfo connectionInfo, ITextFormatter textFormatte
             _textFormatter = textFormatter;
             _subjectFormatter = subjectLineFormatter;
         }
-        
+
         private MimeKit.MimeMessage CreateMailMessage(string payload, string subject)
         {
             var mailMessage = new MimeKit.MimeMessage();
@@ -71,7 +72,7 @@ private MimeKit.MimeMessage CreateMailMessage(string payload, string subject)
             mailMessage.Body = _connectionInfo.IsBodyHtml
                 ? new MimeKit.BodyBuilder { HtmlBody = payload }.ToMessageBody()
                 : new MimeKit.BodyBuilder { TextBody = payload }.ToMessageBody();
-            return mailMessage;            
+            return mailMessage;
         }
 
         /// <summary>
@@ -126,9 +127,13 @@ private SmtpClient OpenConnectedSmtpClient()
                     smtpClient.ServerCertificateValidationCallback += _connectionInfo.ServerCertificateValidationCallback;
                 }
 
-                smtpClient.Connect(
-                    _connectionInfo.MailServer, _connectionInfo.Port,
-                    useSsl: _connectionInfo.EnableSsl);
+                if (_connectionInfo.MailKitSecureSocketOption.HasValue)
+                    smtpClient.Connect(_connectionInfo.MailServer, _connectionInfo.Port,
+                        (SecureSocketOptions) _connectionInfo.MailKitSecureSocketOption.Value);
+                else
+                    smtpClient.Connect(
+                        _connectionInfo.MailServer, _connectionInfo.Port,
+                        useSsl: _connectionInfo.EnableSsl);
 
                 if (_connectionInfo.NetworkCredentials != null)
                 {
@@ -142,4 +147,4 @@ private SmtpClient OpenConnectedSmtpClient()
         }
     }
 }
-#endif
+#endif

src/Serilog.Sinks.Email/Sinks/Email/MailKitSecureSocketOptions.cs

@@ -0,0 +1,36 @@
+namespace Serilog.Sinks.Email.Sinks.Email
+{
+    public enum MailKitSecureSocketOptions
+    {
+        //
+        // Summary:
+        //     No SSL or TLS encryption should be used.
+        None = 0,
+
+        //
+        // Summary:
+        //     Allow the MailKit.IMailService to decide which SSL or TLS options to use (default).
+        //     If the server does not support SSL or TLS, then the connection will continue
+        //     without any encryption.
+        Auto = 1,
+
+        //
+        // Summary:
+        //     The connection should use SSL or TLS encryption immediately.
+        SslOnConnect = 2,
+
+        //
+        // Summary:
+        //     Elevates the connection to use TLS encryption immediately after reading the greeting
+        //     and capabilities of the server. If the server does not support the STARTTLS extension,
+        //     then the connection will fail and a System.NotSupportedException will be thrown.
+        StartTls = 3,
+
+        //
+        // Summary:
+        //     Elevates the connection to use TLS encryption immediately after reading the greeting
+        //     and capabilities of the server, but only if the server supports the STARTTLS
+        //     extension.
+        StartTlsWhenAvailable = 4
+    }
+}