diff --git a/Rnwood.Smtp4dev/ApiModel/Message.cs b/Rnwood.Smtp4dev/ApiModel/Message.cs
index 5ade7ef29..9c6edf5c1 100644
--- a/Rnwood.Smtp4dev/ApiModel/Message.cs
+++ b/Rnwood.Smtp4dev/ApiModel/Message.cs
@@ -183,7 +183,7 @@ internal static string GetPartSource(Message message, string id)
 
         private static MimeEntity GetPart(Message message, string id)
         {
-            MessageEntitySummary part = message.Parts.Flatten(p => p.ChildParts).FirstOrDefault(p => p.Id == id);
+            MessageEntitySummary part = message.Parts.Flatten(p => p.ChildParts).SingleOrDefault(p => p.Id == id);
 
             if (part == null)
             {
diff --git a/Rnwood.Smtp4dev/Controllers/MessagesController.cs b/Rnwood.Smtp4dev/Controllers/MessagesController.cs
index 0cd94d8b1..d7ca4a02e 100644
--- a/Rnwood.Smtp4dev/Controllers/MessagesController.cs
+++ b/Rnwood.Smtp4dev/Controllers/MessagesController.cs
@@ -45,7 +45,7 @@ public IEnumerable<ApiModel.MessageSummary> GetSummaries(string sortColumn = "re
 
 		private DbModel.Message GetDbMessage(Guid id)
 		{
-			return messagesRepository.GetMessages().FirstOrDefault(m => m.Id == id) ??
+			return messagesRepository.GetMessages().SingleOrDefault(m => m.Id == id) ??
 				throw new FileNotFoundException($"Message with id {id} was not found.");
 		}
 
@@ -151,7 +151,7 @@ public string GetMessageHtml(Guid id)
 				{
 					string cid = imageElement.Attributes["src"].Value.Replace("cid:", "", StringComparison.OrdinalIgnoreCase);
 
-					var part = message.Parts.Flatten(p => p.ChildParts).FirstOrDefault(p => p.ContentId == cid);
+					var part = message.Parts.Flatten(p => p.ChildParts).SingleOrDefault(p => p.ContentId == cid);
 
 					imageElement.Attributes["src"].Value = $"api/Messages/{id.ToString()}/part/{part?.Id ?? "notfound"}/content";
 				}
diff --git a/Rnwood.Smtp4dev/Controllers/SessionsController.cs b/Rnwood.Smtp4dev/Controllers/SessionsController.cs
index 056fe7f6d..d7edd8776 100644
--- a/Rnwood.Smtp4dev/Controllers/SessionsController.cs
+++ b/Rnwood.Smtp4dev/Controllers/SessionsController.cs
@@ -39,14 +39,14 @@ public IEnumerable<ApiModel.SessionSummary> GetSummaries()
         [HttpGet("{id}")]
         public ApiModel.Session GetSession(Guid id)
         {
-            Session result = dbContext.Sessions.FirstOrDefault(m => m.Id == id);
+            Session result = dbContext.Sessions.SingleOrDefault(m => m.Id == id);
             return new ApiModel.Session(result);
         }
 
         [HttpGet("{id}/log")]
         public string GetSessionLog(Guid id)
         {
-            Session result = dbContext.Sessions.FirstOrDefault(m => m.Id == id);
+            Session result = dbContext.Sessions.SingleOrDefault(m => m.Id == id);
             return result.Log;
         }
 
diff --git a/Rnwood.Smtp4dev/Rnwood.Smtp4dev.csproj b/Rnwood.Smtp4dev/Rnwood.Smtp4dev.csproj
index 0fb857fd7..75220bc54 100644
--- a/Rnwood.Smtp4dev/Rnwood.Smtp4dev.csproj
+++ b/Rnwood.Smtp4dev/Rnwood.Smtp4dev.csproj
@@ -27,6 +27,7 @@
 		<PackageReference Include="Microsoft.AspNetCore.SignalR" Version="1.1.0" />
 		<PackageReference Include="Microsoft.AspNetCore.SignalR.Core" Version="1.1.0" />
 		<PackageReference Include="Microsoft.AspNetCore.StaticFiles" Version="2.2.0" />
+		<PackageReference Include="Microsoft.EntityFrameworkCore.Analyzers" Version="5.0.5" />
 		<PackageReference Include="Microsoft.EntityFrameworkCore.Design" Version="5.0.5">
 		  <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
 		  <PrivateAssets>all</PrivateAssets>
diff --git a/Rnwood.Smtp4dev/Server/ImapServer.cs b/Rnwood.Smtp4dev/Server/ImapServer.cs
index 003036b71..58e6f3ebf 100644
--- a/Rnwood.Smtp4dev/Server/ImapServer.cs
+++ b/Rnwood.Smtp4dev/Server/ImapServer.cs
@@ -30,7 +30,7 @@ public ImapServer(IMessagesRepository messagesRepository, IOptionsMonitor<Server
 
             using var scope = serviceScopeFactory.CreateScope();
             var dbContext = scope.ServiceProvider.GetService<Smtp4devDbContext>();
-            if (dbContext.ImapState.FirstOrDefault() == null)
+            if (!dbContext.ImapState.Any())
             {
                 dbContext.Add(new ImapState
                 {
@@ -162,7 +162,7 @@ private void Session_Fetch(object sender, IMAP_e_Fetch e)
             {
                 foreach (var msgInfo in e.MessagesInfo)
                 {
-                    var dbMessage = this.messagesRepository.GetMessages().FirstOrDefault(m => m.Id == new Guid(msgInfo.ID));
+                    var dbMessage = this.messagesRepository.GetMessages().SingleOrDefault(m => m.Id == new Guid(msgInfo.ID));
 
                     if (dbMessage != null)
                     {
diff --git a/Rnwood.Smtp4dev/Server/Smtp4devServer.cs b/Rnwood.Smtp4dev/Server/Smtp4devServer.cs
index 8d81f862a..dbdd36780 100644
--- a/Rnwood.Smtp4dev/Server/Smtp4devServer.cs
+++ b/Rnwood.Smtp4dev/Server/Smtp4devServer.cs
@@ -260,8 +260,7 @@ internal Task DeleteSession(Guid id)
             {
                 using var scope = serviceScopeFactory.CreateScope();
                 Smtp4devDbContext dbContext = scope.ServiceProvider.GetService<Smtp4devDbContext>();
-
-                Session session = dbContext.Sessions.FirstOrDefault(s => s.Id == id);
+                Session session = dbContext.Sessions.SingleOrDefault(s => s.Id == id);
                 if (session != null)
                 {
                     dbContext.Sessions.Remove(session);