diff --git a/client.go b/client.go
index 5579a1c..e9f3fac 100644
--- a/client.go
+++ b/client.go
@@ -27,11 +27,18 @@ func sendMail(e *mail.Envelope, config *relayConfig) error {
 	msg.WriteString("\r\n")
 
 	Logger.Infof("starting email send -- from:%s, starttls:%t", e.MailFrom.String(), config.STARTTLS)
+	Logger.Infof("Client Remote IP: %s", e.RemoteIP)
+
 	var err error
 	var conn net.Conn
 	var client *smtp.Client
 	var writer io.WriteCloser
 
+	if AllowedSendersFilter.Blocked(e.RemoteIP) {
+		Logger.Info("Remote IP of " + e.RemoteIP + " not allowed to send email.")
+		return errors.Wrap(err, "Remote IP of "+e.RemoteIP+" not allowed to send email.")
+	}
+
 	tlsconfig := &tls.Config{
 		InsecureSkipVerify: config.SkipVerify, //nolint:gosec
 		ServerName:         config.Server,
diff --git a/go.mod b/go.mod
index c03ae7e..0fd9d35 100644
--- a/go.mod
+++ b/go.mod
@@ -6,6 +6,7 @@ require (
 	github.com/asaskevich/EventBus v0.0.0-20180103000110-68a521d7cbbb // indirect
 	github.com/flashmob/go-guerrilla v1.6.1
 	github.com/go-sql-driver/mysql v1.5.0 // indirect
+	github.com/jpillora/ipfilter v1.2.2
 	github.com/kr/text v0.2.0 // indirect
 	github.com/niemeyer/pretty v0.0.0-20200227124842-a10e7caefd8e // indirect
 	github.com/pkg/errors v0.9.1
diff --git a/go.sum b/go.sum
index 153533d..2940bcc 100644
--- a/go.sum
+++ b/go.sum
@@ -9,6 +9,8 @@ github.com/flashmob/go-guerrilla v1.6.1 h1:MLkqzRFUJveVAWuQ3s2MNPTAWbvXLt8EFsBor
 github.com/flashmob/go-guerrilla v1.6.1/go.mod h1:ZT9TRggRsSY4ZVndoyx8TRUxi3tM/nOYtKWKDX94H0I=
 github.com/go-sql-driver/mysql v1.5.0 h1:ozyZYNQW3x3HtqT1jira07DN2PArx2v7/mN66gGcHOs=
 github.com/go-sql-driver/mysql v1.5.0/go.mod h1:DCzpHaOWr8IXmIStZouvnhqoel9Qv2LBy8hT2VhHyBg=
+github.com/jpillora/ipfilter v1.2.2 h1:lfENG7V1/T+ZutAtSbt6gssvzj3Ql0JmcFlqS/BES2E=
+github.com/jpillora/ipfilter v1.2.2/go.mod h1:xvAYjA+48eM9E5+sg9yI55N5lE9sefckjsnDvSiEA+g=
 github.com/konsorten/go-windows-terminal-sequences v1.0.3 h1:CE8S1cTafDpPvMhIxNJKvHsGVBgn1xWYf1NbHQhywc8=
 github.com/konsorten/go-windows-terminal-sequences v1.0.3/go.mod h1:T0+1ngSBFLxvqU3pZ+m/2kptfBszLMUkC4ZK/EgS/cQ=
 github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
@@ -17,6 +19,8 @@ github.com/kr/text v0.2.0 h1:5Nx0Ya0ZqY2ygV366QzturHI13Jq95ApcVaJBhpS+AY=
 github.com/kr/text v0.2.0/go.mod h1:eLer722TekiGuMkidMxC/pM04lWEeraHUUmBw8l2grE=
 github.com/niemeyer/pretty v0.0.0-20200227124842-a10e7caefd8e h1:fD57ERR4JtEqsWbfPhv4DMiApHyliiK5xCTNVSPiaAs=
 github.com/niemeyer/pretty v0.0.0-20200227124842-a10e7caefd8e/go.mod h1:zD1mROLANZcx1PVRCS0qkT7pwLkGfwJo4zjcN/Tysno=
+github.com/phuslu/iploc v1.0.20200807 h1:LIBm2Y9l5zmUvnJhQgMcLZ0iVwuG+5/L6AgbMwSOpE4=
+github.com/phuslu/iploc v1.0.20200807/go.mod h1:Q/0VX0txvbxekt4NhWIi3Q3eyZ139lHhnlzvDxyXhuc=
 github.com/pkg/errors v0.9.1 h1:FEBLx1zS214owpjy7qsBeixbURkuhQAwrK5UwLGTwt4=
 github.com/pkg/errors v0.9.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
@@ -25,8 +29,11 @@ github.com/sirupsen/logrus v1.6.0 h1:UBcNElsrwanuuMsnGSlYmtmgbb23qDR5dG+6X6Oo89I
 github.com/sirupsen/logrus v1.6.0/go.mod h1:7uNnSEd1DgxDLC74fIahvMZmmYsHGZGEOFrfsX/uA88=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
 github.com/stretchr/testify v1.2.2/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=
+github.com/stretchr/testify v1.4.0/go.mod h1:j7eGeouHqKxXV5pUuKE4zz7dFj8WfuZ+81PSLYec5m4=
 github.com/stretchr/testify v1.5.1 h1:nOGnQDM7FYENwehXlg/kFVnos3rEvtKTjRvOWSzb6H4=
 github.com/stretchr/testify v1.5.1/go.mod h1:5W2xD1RspED5o8YsWQXVCued0rvSQ+mT+I5cxcmMvtA=
+github.com/tomasen/realip v0.0.0-20180522021738-f0c99a92ddce h1:fb190+cK2Xz/dvi9Hv8eCYJYvIGUTN2/KLq1pT6CjEc=
+github.com/tomasen/realip v0.0.0-20180522021738-f0c99a92ddce/go.mod h1:o8v6yHRoik09Xen7gje4m9ERNah1d1PPsVq1VEx9vE4=
 golang.org/x/sys v0.0.0-20190422165155-953cdadca894/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20200515095857-1151b9dac4a9 h1:YTzHMGlqJu67/uEo1lBv0n3wBXhXNeUbB1XfN2vmTm0=
 golang.org/x/sys v0.0.0-20200515095857-1151b9dac4a9/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
diff --git a/main.go b/main.go
index d2939a6..41bb96d 100644
--- a/main.go
+++ b/main.go
@@ -1,6 +1,7 @@
 package main
 
 import (
+	"bufio"
 	"encoding/json"
 	"flag"
 	"fmt"
@@ -10,6 +11,7 @@ import (
 	"syscall"
 
 	log "github.com/flashmob/go-guerrilla/log"
+	"github.com/jpillora/ipfilter"
 )
 
 const (
@@ -23,6 +25,9 @@ const (
 // Logger is the global logger
 var Logger log.Logger
 
+// Global List of Allowed Sender IPs:
+var AllowedSendersFilter = ipfilter.New(ipfilter.Options{})
+
 type mailRelayConfig struct {
 	SMTPServer        string   `json:"smtp_server"`
 	SMTPPort          int      `json:"smtp_port"`
@@ -35,6 +40,7 @@ type mailRelayConfig struct {
 	LocalListenIP     string   `json:"local_listen_ip"`
 	LocalListenPort   int      `json:"local_listen_port"`
 	AllowedHosts      []string `json:"allowed_hosts"`
+	AllowedSenders    string   `json:"allowed_senders"`
 	TimeoutSecs       int      `json:"timeout_secs"`
 }
 
@@ -52,12 +58,16 @@ func run() error {
 	var test bool
 	var testsender string
 	var testrcpt string
+	var checkIP bool
+	var ipToCheck string
 	var verbose bool
 	flag.StringVar(&configFile, "config", "/etc/mailrelay.json", "specifies JSON config file")
 	flag.BoolVar(&test, "test", false, "sends a test message to SMTP server")
 	flag.StringVar(&testsender, "sender", "", "used with 'test' to specify sender email address")
 	flag.StringVar(&testrcpt, "rcpt", "", "used with 'test' to specify recipient email address")
 	flag.BoolVar(&verbose, "verbose", false, "verbose output")
+	flag.BoolVar(&checkIP, "checkIP", false, "Checks a provided IP address to see if it would be allowed")
+	flag.StringVar(&ipToCheck, "ip", "", "used with 'checkIP' to specify IP address to test")
 	flag.Parse()
 
 	appConfig, err := loadConfig(configFile)
@@ -66,6 +76,34 @@ func run() error {
 		return fmt.Errorf("loading config: %w", err)
 	}
 
+	if appConfig.AllowedSenders != "*" {
+		file, err := os.Open(appConfig.AllowedSenders)
+
+		if err != nil {
+			return fmt.Errorf("failed opening file: %s", err)
+		}
+
+		scanner := bufio.NewScanner(file)
+		scanner.Split(bufio.ScanLines)
+		var allowedIPsAndRanges []string
+
+		for scanner.Scan() {
+			allowedIPsAndRanges = append(allowedIPsAndRanges, scanner.Text())
+		}
+
+		file.Close()
+
+		for _, eachline := range allowedIPsAndRanges {
+			fmt.Println(eachline)
+		}
+
+		AllowedSendersFilter = ipfilter.New(ipfilter.Options{
+			//AllowedIPs:     []string{"192.168.0.0/24"},
+			AllowedIPs:     allowedIPsAndRanges,
+			BlockByDefault: true,
+		})
+	}
+
 	err = Start(appConfig, verbose)
 	if err != nil {
 		flag.Usage()
@@ -89,6 +127,11 @@ func run() error {
 		return nil
 	}
 
+	if checkIP {
+		Logger.Infof("Checking to see if %s is allowed to send email: %t", ipToCheck, AllowedSendersFilter.Allowed(ipToCheck))
+		return nil
+	}
+
 	// Wait for SIGINT
 	c := make(chan os.Signal, 1)
 	signal.Notify(c, os.Interrupt, syscall.SIGTERM)
@@ -124,6 +167,7 @@ func configDefaults(config *mailRelayConfig) {
 	config.LocalListenIP = DefaultLocalListenIP
 	config.LocalListenPort = DefaultLocalListenPort
 	config.AllowedHosts = []string{"*"}
+	config.AllowedSenders = "*"
 	config.TimeoutSecs = DefaultTimeoutSecs
 }