SharePoint Get all users emal from SPUser objec

        public static string strLDAP = "LDAP://Test.com";

        public static void GetADMails(ref List<string> list, string strLoginName)
        {
            DirectoryEntry newEntry = new DirectoryEntry(strLDAP);
            strLoginName = strLoginName.Substring(strLoginName.LastIndexOf('\\') + 1);
            DirectorySearcher newSearcher = new DirectorySearcher(newEntry, "(&(objectClass=group)(CN=" + strLoginName + "))");
            SearchResult sr = newSearcher.FindOne();
            if (sr != null)
            {
                foreach (string srUser in sr.GetDirectoryEntry().Properties["member"])
                {
                    DirectoryEntry tmpEntry = new DirectoryEntry("LDAP://" + srUser);
                    if (tmpEntry.Properties["objectClass"][1].ToString() == "person")
                    {
                        if (string.IsNullOrEmpty(ConvertNull(tmpEntry.InvokeGet("Mail")).Trim()) || list.Contains(ConvertNull(tmpEntry.InvokeGet("Mail")).Trim()))
                        {
                            continue;
                        }
                        Console.WriteLine(tmpEntry.InvokeGet("Mail"));
                        list.Add(ConvertNull(tmpEntry.InvokeGet("Mail")).Trim());
                    }
                    else
                    {
                        GetADMails(ref list, tmpEntry.InvokeGet("sAMAccountName").ToString());
                    }
                }
            }
            else
            {
                newSearcher = new DirectorySearcher(newEntry, "(&(&(objectCategory=person)(objectClass=user))(cn=" + strLoginName + "))");
                sr = newSearcher.FindOne();
                if (sr != null)
                {
                    object obj = sr.Properties["Mail"][0];
                    if (!(string.IsNullOrEmpty(ConvertNull(obj).Trim()) || list.Contains(ConvertNull(obj).Trim())))
                    {
                        list.Add(ConvertNull(obj).Trim());
                    }
                }
            }
        }

        public static List<string> GetUserMailsByUserField(SPWeb web, object obj)
        {
            List<string> mailarr = new List<string>();
            SPGroup group = null;
            if (obj == null)
            {
                return mailarr;
            }
            try
            {
                SPFieldUserValueCollection approversCollection;
                web.AllowUnsafeUpdates = true;
                approversCollection = (SPFieldUserValueCollection)obj;
                foreach (SPFieldUserValue spFieldUserValue in approversCollection)
                {
                    if (spFieldUserValue.User == null)
                    {
                        //sharepoitn group 
                        try
                        {
                            group = web.SiteGroups[spFieldUserValue.LookupValue];
                            SPUserCollection users = group.Users;
                            foreach (SPUser user in users)
                            {
                                if (user.ID == group.Owner.ID)
                                {
                                    continue;
                                }
                                if (string.IsNullOrEmpty(ConvertNull(user.Email)))
                                {
                                    continue;
                                }
                                if (mailarr.Contains(ConvertNull(user.Email).Trim()))
                                {
                                    continue;
                                }
                                mailarr.Add(ConvertNull(user.Email).Trim());
                            }
                        }
                        catch { }
                    }
                    else
                    {
                        //sharepoint user or ad group
                        try
                        {
                            GetADMails(ref mailarr, web.AllUsers.GetByID(spFieldUserValue.LookupId).LoginName);
                        }
                        catch { }
                    }
                }
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }
            return mailarr;

        }

List<string> maillist= GetUserMailsByUserField(web, item["Reader"]);