From f2eeaa01df6a7066a2f84161170fe38d1977a5c4 Mon Sep 17 00:00:00 2001
From: Jeffrey Stedfast <jestedfa@microsoft.com>
Date: Fri, 6 Sep 2024 10:34:46 -0400
Subject: [PATCH] Updated FAQ.md to add a Q/A for TypeLoadException issues

---
 FAQ.md | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/FAQ.md b/FAQ.md
index ed952e2126..91102c9874 100644
--- a/FAQ.md
+++ b/FAQ.md
@@ -6,6 +6,7 @@
 
 * [Are MimeKit and MailKit completely free? Can I use them in my proprietary product(s)?](#completely-free)
 * [Why do I get `NotSupportedException: No data is available for encoding ######. For information on defining a custom encoding, see the documentation for the Encoding.RegisterProvider method.`?](#register-provider)
+* [Why do I get a `TypeLoadException` when I try to create a new MimeMessage?](#type-load-exception)
 
 ### Messages
 
@@ -47,6 +48,34 @@ the following line of code to your program initialization (e.g. the beginning of
 System.Text.Encoding.RegisterProvider (System.Text.CodePagesEncodingProvider.Instance);
 ```
 
+### <a name="type-load-exception">Q: Why do I get a `TypeLoadException` when I try to create a new MimeMessage?</a>
+
+This only seems to happen in cases where the application is built for .NET Framework (v4.x) and seems to be most
+common for ASP.NET web applications that were built using Visual Studio 2019 (it is unclear whether this happens
+with Visual Studio 2022 as well).
+
+The issue is that some (older?) versions of MSBuild do not correctly generate `\*.dll.config`, `app.config`
+and/or `web.config` files with proper assembly version binding redirects.
+
+If this problem is happening to you, make sure to use MimeKit and MailKit >= v4.0 which include `MimeKit.dll.config`
+and `MailKit.dll.config`.
+
+The next step is to manually edit your application's `app.config` (or `web.config`) to add a binding redirect
+for `System.Runtime.CompilerServices.Unsafe`:
+
+```xml
+<configuration>
+  <runtime>
+    <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
+      <dependentAssembly>
+        <assemblyIdentity name="System.Runtime.CompilerServices.Unsafe" publicKeyToken="b03f5f7f11d50a3a" culture="neutral" />
+        <bindingRedirect oldVersion="0.0.0.0-6.0.0.0" newVersion="6.0.0.0" />
+      </dependentAssembly>
+    </assemblyBinding>
+  </runtime>
+</configuration>
+```
+
 ## Messages
 
 ### <a name="create-attachments">Q: How do I create a message with attachments?</a>