Added IMimeEntity, IMimePart, IMultipart and IMessagePart interfaces

More fixes for issue #980

MimeKit/IMessagePart.cs

@@ -0,0 +1,47 @@
+//
+// IMessagePart.cs
+//
+// Author: Jeffrey Stedfast <[email protected]>
+//
+// Copyright (c) 2013-2023 .NET Foundation and Contributors
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+//
+
+namespace MimeKit {
+	/// <summary>
+	/// An interface for a MIME part containing a <see cref="MimeMessage"/> as its content.
+	/// </summary>
+	/// <remarks>
+	/// Represents MIME entities such as those with a Content-Type of message/rfc822 or message/news.
+	/// </remarks>
+	public interface IMessagePart : IMimeEntity
+	{
+		/// <summary>
+		/// Gets or sets the message content.
+		/// </summary>
+		/// <remarks>
+		/// Gets or sets the message content.
+		/// </remarks>
+		/// <value>The message content.</value>
+		MimeMessage Message {
+			get; set;
+		}
+	}
+}