From ca0751cb0fbde40764852151235fc5a642e58107 Mon Sep 17 00:00:00 2001
From: Jeffrey Stedfast <jestedfa@microsoft.com>
Date: Tue, 27 Jul 2021 11:59:55 -0400
Subject: [PATCH] If an invalid INTERNALDATE is encountered, just use
 DateTimeOffset.MinValue

Do not throw a FormatException.

Fixes issue #1236
---
 MailKit/Net/Imap/ImapUtils.cs        | 21 ++++++++-------------
 UnitTests/Net/Imap/ImapUtilsTests.cs |  3 ++-
 2 files changed, 10 insertions(+), 14 deletions(-)

diff --git a/MailKit/Net/Imap/ImapUtils.cs b/MailKit/Net/Imap/ImapUtils.cs
index cffd50aa10..e2f9fec318 100644
--- a/MailKit/Net/Imap/ImapUtils.cs
+++ b/MailKit/Net/Imap/ImapUtils.cs
@@ -195,11 +195,6 @@ static bool TryGetTimeZone (string text, ref int index, out TimeSpan timezone)
 			return true;
 		}
 
-		static Exception InvalidInternalDateFormat (string text)
-		{
-			return new FormatException ("Invalid INTERNALDATE format: " + text);
-		}
-
 		/// <summary>
 		/// Parses the internal date string.
 		/// </summary>
@@ -215,37 +210,37 @@ public static DateTimeOffset ParseInternalDate (string text)
 				index++;
 
 			if (index >= text.Length || !TryGetInt32 (text, ref index, '-', out day) || day < 1 || day > 31)
-				throw InvalidInternalDateFormat (text);
+				return DateTimeOffset.MinValue;
 
 			index++;
 			if (index >= text.Length || !TryGetMonth (text, ref index, '-', out month))
-				throw InvalidInternalDateFormat (text);
+				return DateTimeOffset.MinValue;
 
 			index++;
 			if (index >= text.Length || !TryGetInt32 (text, ref index, ' ', out year) || year < 1969)
-				throw InvalidInternalDateFormat (text);
+				return DateTimeOffset.MinValue;
 
 			index++;
 			if (index >= text.Length || !TryGetInt32 (text, ref index, ':', out hour) || hour > 23)
-				throw InvalidInternalDateFormat (text);
+				return DateTimeOffset.MinValue;
 
 			index++;
 			if (index >= text.Length || !TryGetInt32 (text, ref index, ':', out minute) || minute > 59)
-				throw InvalidInternalDateFormat (text);
+				return DateTimeOffset.MinValue;
 
 			index++;
 			if (index >= text.Length || !TryGetInt32 (text, ref index, ' ', out second) || second > 59)
-				throw InvalidInternalDateFormat (text);
+				return DateTimeOffset.MinValue;
 
 			index++;
 			if (index >= text.Length || !TryGetTimeZone (text, ref index, out timezone))
-				throw InvalidInternalDateFormat (text);
+				return DateTimeOffset.MinValue;
 
 			while (index < text.Length && char.IsWhiteSpace (text[index]))
 				index++;
 
 			if (index < text.Length)
-				throw InvalidInternalDateFormat (text);
+				return DateTimeOffset.MinValue;
 
 			// return DateTimeOffset.ParseExact (text.Trim (), "d-MMM-yyyy HH:mm:ss zzz", CultureInfo.InvariantCulture.DateTimeFormat);
 			return new DateTimeOffset (year, month, day, hour, minute, second, timezone);
diff --git a/UnitTests/Net/Imap/ImapUtilsTests.cs b/UnitTests/Net/Imap/ImapUtilsTests.cs
index 8f5752b53d..6ea54aaeed 100644
--- a/UnitTests/Net/Imap/ImapUtilsTests.cs
+++ b/UnitTests/Net/Imap/ImapUtilsTests.cs
@@ -165,6 +165,7 @@ public void TestFormattingReversedUids ()
 		public void TestParseInvalidInternalDates ()
 		{
 			var internalDates = new string [] {
+				"00-Jan-0000 00:00:00 +0000", // Note: This example is taken from an actual response from a Domino IMAP server. Likely represents an uninitialized value.
 				"98765432100-OCT-2018 13:41:57 -0400",
 				"27-JAG-2018 13:41:57 -0400",
 				"27-OCT-1909 13:41:57 -0400",
@@ -176,7 +177,7 @@ public void TestParseInvalidInternalDates ()
 			};
 
 			foreach (var internalDate in internalDates)
-				Assert.Throws<FormatException> (() => ImapUtils.ParseInternalDate (internalDate), internalDate);
+				Assert.AreEqual (DateTimeOffset.MinValue, ImapUtils.ParseInternalDate (internalDate), internalDate);
 		}
 
 		[Test]