Custom routing agent based on sender's security group and subject

Question

I made a custom routing agent that routes mails contains the word [encrypt] in the subject and sent from domain test.com
The part of the code is
if (e.MailItem.FromAddress.DomainPart.Contains("test.com")
                && e.MailItem.Message.Subject.Contains("[encrypt]"))
now what i need is to route mails based on the membership of a certain security group like "securemail" not the whole domain. ie if the sender is a member in security group (securemail) and the subject contains the word [encrypt] route the mail
Thanks

Answer 1

Thanks for your answer Glen
The following  code is on exchange 2010 but i need it to check for a security group membership if possible
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Microsoft.Exchange.Data.Transport;
using Microsoft.Exchange.Data.Transport.Email;
using Microsoft.Exchange.Data.Transport.Smtp;
using Microsoft.Exchange.Data.Transport.Routing;
using Microsoft.Exchange.Data.Common;
namespace RoutingAgentOverride
    public class SampleRoutingAgentFactory : RoutingAgentFactory
        public override RoutingAgent CreateAgent(SmtpServer server)
            RoutingAgent myAgent = new ownRoutingAgent();
            return myAgent;
public class ownRoutingAgent : RoutingAgent
    public ownRoutingAgent()
        //subscribe to different events
        base.OnResolvedMessage += new ResolvedMessageEventHandler(ownRoutingAgent_OnResolvedMessage);
    void ownRoutingAgent_OnResolvedMessage(ResolvedMessageEventSource source, QueuedMessageEventArgs e)
        try
            // For testing purposes we do not only check the sender address but the subject line as well
            // If the subject contains the substring "REDIR" then the default routing is overwritten.
            // Instead of hard-coding the sender you could also perform an LDAP-query, read the information
            // from a text file, etc.
            if (e.MailItem.FromAddress.DomainPart.Contains("contoso.com")
                && e.MailItem.Message.Subject.Contains("[encrypt]"))
                // Here we set the address space we want to use for the next hop. Note that this doesn't change the recipient address.
                // Setting the routing domain to "nexthopdomain.com" only means that the routing engine chooses a suitable connector
                // for nexthopdomain.com instead of using the recpient's domain.
                RoutingDomain myRoutingOverride = new RoutingDomain("nexthopdomain.com");
                foreach (EnvelopeRecipient recp in e.MailItem.Recipients)
                    recp.SetRoutingOverride(myRoutingOverride);
        catch // (Exception except)