E-Mail Validierung hinzugefügt

AMWD.Common/AMWD.Common.csproj

@@ -36,6 +36,7 @@
   </ItemGroup>
 
   <ItemGroup>
+    <PackageReference Include="DnsClient" Version="1.5.0" />
     <PackageReference Include="Newtonsoft.Json" Version="10.0.1" />
     <PackageReference Include="Unclassified.DeepConvert" Version="1.3.0" />
     <PackageReference Include="Unclassified.NetRevisionTask" Version="0.4.1">

AMWD.Common/Extensions/StringExtensions.cs

@@ -1,8 +1,11 @@
 using System.Collections.Generic;
 using System.Globalization;
 using System.Linq;
+using System.Net;
+using System.Net.Mail;
 using System.Text;
 using System.Text.RegularExpressions;
+using DnsClient;
 
 namespace System
 {
@@ -137,5 +140,50 @@ namespace System
 
 			return decimal.Parse(decString, culture);
 		}
+
+		/// <summary>
+		/// Checks whether the given <see cref="string"/> is a valid <see cref="MailAddress"/>.
+		/// </summary>
+		/// <remarks>
+		/// You can enhance the check by requesting the MX record of the domain.
+		/// </remarks>
+		/// <param name="email">The email address as string to validate.</param>
+		/// <param name="checkRecordExists">A value indicating whether to resolve a MX record.</param>
+		/// <returns><c>true</c> when the email address is valid, other wise <c>false</c>.</returns>
+		public static bool IsValidEmailAddress(this string email, bool checkRecordExists = false)
+			=> email.IsValidEmailAddress(checkRecordExists ? new LookupClient() : null);
+
+		/// <summary>
+		/// Checks whether the given <see cref="string"/> is a valid <see cref="MailAddress"/>.
+		/// </summary>
+		/// <remarks>
+		/// The check is enhanced by a request for MX records on the defined <paramref name="nameservers"/>.
+		/// </remarks>
+		/// <param name="email">The email address as string to validate.</param>
+		/// <param name="nameservers">A list of <see cref="IPEndPoint"/>s of nameservers.</param>
+		/// <returns><c>true</c> when the email address is valid, other wise <c>false</c>.</returns>
+		public static bool IsValidEmailAddress(this string email, IEnumerable<IPEndPoint> nameservers)
+			=> email.IsValidEmailAddress(new LookupClient(nameservers.ToArray()));
+
+		private static bool IsValidEmailAddress(this string email, LookupClient lookupClient)
+		{
+			try
+			{
+				var mailAddress = new MailAddress(email);
+				bool isValid = mailAddress.Address == email;
+
+				if (isValid && lookupClient != null)
+				{
+					var result = lookupClient.Query(mailAddress.Host, QueryType.MX);
+					isValid &= result.Answers.MxRecords().Any();
+				}
+
+				return isValid;
+			}
+			catch
+			{
+				return false;
+			}
+		}
 	}
 }