Added an ITextRfc822Headers interface

MimeKit/ITextRfc822Headers.cs

@@ -0,0 +1,37 @@
+//
+// ITextRfc822Headers.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 message headers as its content.
+	/// </summary>
+	/// <remarks>
+	/// Represents MIME entities with a Content-Type of text/rfc822-headers.
+	/// </remarks>
+	public interface ITextRfc822Headers : IMessagePart
+	{
+	}
+}

MimeKit/TextRfc822Headers.cs

@@ -33,7 +33,7 @@ namespace MimeKit {
 	/// <remarks>
 	/// Represents MIME entities with a Content-Type of text/rfc822-headers.
 	/// </remarks>
-	public class TextRfc822Headers : MessagePart
+	public class TextRfc822Headers : MessagePart, ITextRfc822Headers
 	{
 		/// <summary>
 		/// Initialize a new instance of the <see cref="TextRfc822Headers"/> class.