Add EICAR test file send via --eicar flag

eicar.go

@@ -0,0 +1,70 @@
+package main
+
+import (
+	"fmt"
+	"net/smtp"
+)
+
+type eicarResult struct {
+	sent   bool
+	result string
+}
+
+// eicarString assembles the EICAR test string at runtime to avoid static AV detection.
+func eicarString() string {
+	p1 := `X5O!P%@AP[4\PZX54(P^)7CC)7}`
+	p2 := `$EICAR-STANDARD-ANTIVIRUS-TEST-FILE!$H+H*`
+	return p1 + p2
+}
+
+// sendEICAR sends the EICAR test file as an email attachment to the target mail server.
+// A virus filter that detects it will reject the message; sent=true means it was accepted.
+func sendEICAR(mailFrom string, mailTo string, targetHost string, targetPort string) (eicarResult, error) {
+	var er eicarResult
+
+	c, err := smtp.Dial(targetHost + ":" + targetPort)
+	if err != nil {
+		return er, err
+	}
+	defer c.Quit() //nolint:errcheck
+
+	if err = c.Mail(mailFrom); err != nil {
+		er.result = err.Error()
+		return er, nil
+	}
+
+	if err = c.Rcpt(mailTo); err != nil {
+		er.result = err.Error()
+		return er, nil
+	}
+
+	wc, err := c.Data()
+	if err != nil {
+		return er, err
+	}
+
+	body := "MIME-Version: 1.0\r\n" +
+		"Content-Type: multipart/mixed; boundary=\"eicartest\"\r\n" +
+		"Subject: EICAR AV Test\r\n" +
+		"From: " + mailFrom + "\r\n" +
+		"To: " + mailTo + "\r\n\r\n" +
+		"--eicartest\r\n" +
+		"Content-Type: application/octet-stream\r\n" +
+		"Content-Disposition: attachment; filename=\"eicar.com\"\r\n\r\n" +
+		eicarString() + "\r\n" +
+		"--eicartest--\r\n"
+
+	if _, err = fmt.Fprint(wc, body); err != nil {
+		er.result = err.Error()
+		wc.Close() //nolint:errcheck
+		return er, nil
+	}
+
+	if err = wc.Close(); err != nil {
+		er.result = err.Error()
+		return er, nil
+	}
+
+	er.sent = true
+	return er, nil
+}

main.go

@@ -58,13 +58,15 @@ type mxresult struct {
 	smtps            bool
 	openrelay        bool
 	vrfysupport      bool
+	eicardelivered   bool
 	smugglevuln      bool
 	smuggleresp      string
 	smuggleerror     string
 }
 
 func main() {
 	blacklist := flag.BoolP("blacklist", "b", false, "Check if the service is on blacklists")
+	eicar := flag.BoolP("eicar", "e", false, "Send EICAR test file to check AV filtering (use only on servers you are authorized to test)")
 	dkimSelector := flag.StringP("dkim-selector", "S", "",
 		"The DKIM selector. If set a DKIM check is performed on the provided service domain")
 	dnsServer := flag.StringP("dnsserver", "d", "8.8.8.8", "The dns server to be requested")
@@ -396,6 +398,23 @@ func main() {
 						printOK("Server is not an open relay")
 					}
 
+					// EICAR test
+					if *eicar {
+						printSection("EICAR AV Test")
+						er, err := sendEICAR(*mailFrom, *mailTo, targetHost, port)
+						if err != nil {
+							printError(err.Error())
+						} else if er.sent {
+							singlemx.eicardelivered = true
+							printInfo("EICAR test file", "accepted by server")
+						} else {
+							printInfo("EICAR test file", "rejected by server")
+							if len(er.result) > 0 {
+								printInfo("Response", er.result)
+							}
+						}
+					}
+
 					// STARTTLS test
 					printSection("STARTTLS")
 					singlemx.starttls = orresult.starttlsbool