diff --git a/UnitTests/Net/Imap/ImapClientTests.cs b/UnitTests/Net/Imap/ImapClientTests.cs
index cb0263acf3..3b28be8206 100644
--- a/UnitTests/Net/Imap/ImapClientTests.cs
+++ b/UnitTests/Net/Imap/ImapClientTests.cs
@@ -332,7 +332,7 @@ static Socket Connect (string host, int port)
 		[Test]
 		public void TestSslHandshakeExceptions ()
 		{
-			using (var client = new ImapClient () { TagPrefix = 'A' }) {
+			using (var client = new ImapClient ()) {
 				Socket socket;
 
 				// 1. Test connecting to a non-SSL port fails with an SslHandshakeException.
@@ -376,7 +376,7 @@ public void TestSslHandshakeExceptions ()
 		[Test]
 		public async Task TestSslHandshakeExceptionsAsync ()
 		{
-			using (var client = new ImapClient () { TagPrefix = 'A' }) {
+			using (var client = new ImapClient ()) {
 				Socket socket;
 
 				// 1. Test connecting to a non-SSL port fails with an SslHandshakeException.
@@ -417,6 +417,21 @@ public async Task TestSslHandshakeExceptionsAsync ()
 			}
 		}
 
+		[Test]
+		public void TestStartTlsNotSupported ()
+		{
+			var commands = new List<ImapReplayCommand> {
+				new ImapReplayCommand ("", "common.basic-greeting.txt"),
+				new ImapReplayCommand ("A00000000 CAPABILITY\r\n", "common.capability.txt"),
+			};
+
+			using (var client = new ImapClient () { TagPrefix = 'A' })
+				Assert.Throws<NotSupportedException> (() => client.Connect (new ImapReplayStream (commands, false), "localhost", 143, SecureSocketOptions.StartTls), "STARTTLS");
+
+			using (var client = new ImapClient () { TagPrefix = 'A' })
+				Assert.ThrowsAsync<NotSupportedException> (() => client.ConnectAsync (new ImapReplayStream (commands, true), "localhost", 143, SecureSocketOptions.StartTls), "STARTTLS Async");
+		}
+
 		[Test]
 		public void TestProtocolLoggerExceptions ()
 		{
diff --git a/UnitTests/Net/Imap/Resources/common/basic-greeting.txt b/UnitTests/Net/Imap/Resources/common/basic-greeting.txt
new file mode 100644
index 0000000000..646f85c067
--- /dev/null
+++ b/UnitTests/Net/Imap/Resources/common/basic-greeting.txt
@@ -0,0 +1 @@
+* OK IMAP4 server ready.
diff --git a/UnitTests/Net/Pop3/Pop3ClientTests.cs b/UnitTests/Net/Pop3/Pop3ClientTests.cs
index 8db6a099f3..3ad70697cf 100644
--- a/UnitTests/Net/Pop3/Pop3ClientTests.cs
+++ b/UnitTests/Net/Pop3/Pop3ClientTests.cs
@@ -571,6 +571,21 @@ public async Task TestInvalidStateExceptionsAsync ()
 			}
 		}
 
+		[Test]
+		public void TestStartTlsNotSupported ()
+		{
+			var commands = new List<Pop3ReplayCommand> {
+				new Pop3ReplayCommand ("", "comcast.greeting.txt"),
+				new Pop3ReplayCommand ("CAPA\r\n", "comcast.err.txt")
+			};
+
+			using (var client = new Pop3Client ())
+				Assert.Throws<NotSupportedException> (() => client.Connect (new Pop3ReplayStream (commands, false), "localhost", 110, SecureSocketOptions.StartTls), "STLS");
+
+			using (var client = new Pop3Client ())
+				Assert.ThrowsAsync<NotSupportedException> (() => client.ConnectAsync (new Pop3ReplayStream (commands, true), "localhost", 110, SecureSocketOptions.StartTls), "STLS Async");
+		}
+
 		[Test]
 		public void TestProtocolLoggerExceptions ()
 		{
@@ -1671,6 +1686,7 @@ public void TestProbedUidlSupportError ()
 				Assert.AreEqual (1800662, client.Size, "Expected 1800662 octets");
 
 				Assert.Throws<NotSupportedException> (() => client.GetMessageUids ());
+				Assert.Throws<NotSupportedException> (() => client.GetMessageUid (0));
 
 				try {
 					client.Disconnect (true);
@@ -1723,6 +1739,7 @@ public async Task TestProbedUidlSupportErrorAsync ()
 				Assert.AreEqual (1800662, client.Size, "Expected 1800662 octets");
 
 				Assert.ThrowsAsync<NotSupportedException> (() => client.GetMessageUidsAsync ());
+				Assert.ThrowsAsync<NotSupportedException> (() => client.GetMessageUidAsync (0));
 
 				try {
 					await client.DisconnectAsync (true);
diff --git a/UnitTests/Net/Smtp/SmtpClientTests.cs b/UnitTests/Net/Smtp/SmtpClientTests.cs
index 610824d70f..3a9bd6b6b8 100644
--- a/UnitTests/Net/Smtp/SmtpClientTests.cs
+++ b/UnitTests/Net/Smtp/SmtpClientTests.cs
@@ -659,6 +659,22 @@ public async Task TestInvalidStateExceptionsAsync ()
 			}
 		}
 
+		[Test]
+		public void TestStartTlsNotSupported ()
+		{
+			var commands = new List<SmtpReplayCommand> {
+				new SmtpReplayCommand ("", "comcast-greeting.txt"),
+				new SmtpReplayCommand ("EHLO unit-tests.mimekit.org\r\n", "ehlo-failed.txt"),
+				new SmtpReplayCommand ("HELO unit-tests.mimekit.org\r\n", "helo.txt"),
+			};
+
+			using (var client = new SmtpClient () { LocalDomain = "unit-tests.mimekit.org" })
+				Assert.Throws<NotSupportedException> (() => client.Connect (new SmtpReplayStream (commands, false), "localhost", 25, SecureSocketOptions.StartTls), "STARTTLS");
+
+			using (var client = new SmtpClient () { LocalDomain = "unit-tests.mimekit.org" })
+				Assert.ThrowsAsync<NotSupportedException> (() => client.ConnectAsync (new SmtpReplayStream (commands, true), "localhost", 25, SecureSocketOptions.StartTls), "STARTTLS Async");
+		}
+
 		[Test]
 		public void TestServiceNotReady ()
 		{
diff --git a/UnitTests/UnitTests.csproj b/UnitTests/UnitTests.csproj
index 0cc32f0d6c..aea94cb88b 100644
--- a/UnitTests/UnitTests.csproj
+++ b/UnitTests/UnitTests.csproj
@@ -146,6 +146,7 @@
     <EmbeddedResource Include="Net\Imap\Resources\acl\getacl.txt" />
     <EmbeddedResource Include="Net\Imap\Resources\acl\listrights.txt" />
     <EmbeddedResource Include="Net\Imap\Resources\acl\myrights.txt" />
+    <EmbeddedResource Include="Net\Imap\Resources\common\basic-greeting.txt" />
     <EmbeddedResource Include="Net\Imap\Resources\common\capability.txt" />
     <EmbeddedResource Include="Net\Imap\Resources\common\capability-greeting.txt" />
     <EmbeddedResource Include="Net\Imap\Resources\common\fetch-annotations.txt" />