diff --git a/go/ql/lib/semmle/go/frameworks/Email.qll b/go/ql/lib/semmle/go/frameworks/Email.qll
index a1d43d3c397..d7744951c08 100644
--- a/go/ql/lib/semmle/go/frameworks/Email.qll
+++ b/go/ql/lib/semmle/go/frameworks/Email.qll
@@ -26,9 +26,14 @@ module EmailData {
   private class SmtpData extends Range {
     SmtpData() {
       // func (c *Client) Data() (io.WriteCloser, error)
-      exists(Method data |
+      exists(Method data, DataFlow::Node n |
         data.hasQualifiedName("net/smtp", "Client", "Data") and
-        this.(DataFlow::SsaNode).getInit() = data.getACall().getResult(0)
+        // Deal with cases like
+        //   w, _ := s.Data()
+        //   io.WriteString(w, source()) // $ Alert
+        //   w.Write(source())           // $ Alert
+        DataFlow::localFlow(data.getACall().getResult(0), n) and
+        this.(DataFlow::PostUpdateNode).getPreUpdateNode() = n
       )
       or
       // func SendMail(addr string, a Auth, from string, to []string, msg []byte) error
@@ -98,3 +103,18 @@ private class MultipartNewWriterModel extends TaintTracking::FunctionModel {
     input.isResult() and output.isParameter(0)
   }
 }
+// /**
+//  * A taint model of the `Data` method of `Client` from `net/smtp`.
+//  *
+//  * If tainted data is written to the writer created by this method, the client
+//  * should be considered tainted as well.
+//  */
+// private class SmtpClientDataModel extends TaintTracking::FunctionModel, Method {
+//   SmtpClientDataModel() {
+//     // func (c *Client) Data() (io.WriteCloser, error)
+//     this.hasQualifiedName("net/smtp", "Client", "Data")
+//   }
+//   override predicate hasTaintFlow(FunctionInput input, FunctionOutput output) {
+//     input.isResult(0) and output.isReceiver()
+//   }
+// }
diff --git a/go/ql/test/library-tests/semmle/go/frameworks/Email/EmailData.expected b/go/ql/test/library-tests/semmle/go/frameworks/Email/EmailData.expected
index 070800dab63..3324ee56033 100644
--- a/go/ql/test/library-tests/semmle/go/frameworks/Email/EmailData.expected
+++ b/go/ql/test/library-tests/semmle/go/frameworks/Email/EmailData.expected
@@ -1,7 +1,4 @@
 | mail.go:15:73:15:94 | type conversion |
-| mail.go:18:19:18:23 | definition of write |
-| mail.go:18:19:18:38 | ... := ...[0] |
-| mail.go:20:17:20:21 | write |
 | mail.go:20:17:20:21 | write [postupdate] |
 | mail.go:26:49:26:52 | text |
 | mail.go:26:76:26:79 | text |
diff --git a/go/ql/test/query-tests/Security/CWE-640/EmailInjection.expected b/go/ql/test/query-tests/Security/CWE-640/EmailInjection.expected
index 06f61ee8956..aa4b4914c18 100644
--- a/go/ql/test/query-tests/Security/CWE-640/EmailInjection.expected
+++ b/go/ql/test/query-tests/Security/CWE-640/EmailInjection.expected
@@ -1,6 +1,7 @@
 #select
 | EmailBad.go:12:56:12:67 | type conversion | EmailBad.go:9:10:9:17 | selection of Header | EmailBad.go:12:56:12:67 | type conversion | Email content may contain $@. | EmailBad.go:9:10:9:17 | selection of Header | untrusted input |
 | main.go:33:57:33:78 | type conversion | main.go:31:21:31:31 | call to Referer | main.go:33:57:33:78 | type conversion | Email content may contain $@. | main.go:31:21:31:31 | call to Referer | untrusted input |
+| main.go:43:18:43:22 | write [postupdate] | main.go:39:21:39:31 | call to Referer | main.go:43:18:43:22 | write [postupdate] | Email content may contain $@. | main.go:39:21:39:31 | call to Referer | untrusted input |
 | main.go:54:46:54:59 | untrustedInput | main.go:48:21:48:31 | call to Referer | main.go:54:46:54:59 | untrustedInput | Email content may contain $@. | main.go:48:21:48:31 | call to Referer | untrusted input |
 | main.go:55:52:55:65 | untrustedInput | main.go:48:21:48:31 | call to Referer | main.go:55:52:55:65 | untrustedInput | Email content may contain $@. | main.go:48:21:48:31 | call to Referer | untrusted input |
 | main.go:65:16:65:22 | content | main.go:60:21:60:31 | call to Referer | main.go:65:16:65:22 | content | Email content may contain $@. | main.go:60:21:60:31 | call to Referer | untrusted input |
@@ -11,10 +12,14 @@
 | main.go:95:16:95:23 | content2 | main.go:84:21:84:31 | call to Referer | main.go:95:16:95:23 | content2 | Email content may contain $@. | main.go:84:21:84:31 | call to Referer | untrusted input |
 | main.go:124:57:124:65 | call to Bytes | main.go:113:21:113:31 | call to Referer | main.go:124:57:124:65 | call to Bytes | Email content may contain $@. | main.go:113:21:113:31 | call to Referer | untrusted input |
 | main.go:141:57:141:65 | call to Bytes | main.go:129:21:129:31 | call to Referer | main.go:141:57:141:65 | call to Bytes | Email content may contain $@. | main.go:129:21:129:31 | call to Referer | untrusted input |
+| main.go:151:3:151:3 | w [postupdate] | main.go:146:22:146:32 | call to Referer | main.go:151:3:151:3 | w [postupdate] | Email content may contain $@. | main.go:146:22:146:32 | call to Referer | untrusted input |
+| main.go:152:3:152:3 | w [postupdate] | main.go:147:22:147:32 | call to Referer | main.go:152:3:152:3 | w [postupdate] | Email content may contain $@. | main.go:147:22:147:32 | call to Referer | untrusted input |
 edges
-| EmailBad.go:9:10:9:17 | selection of Header | EmailBad.go:9:10:9:29 | call to Get | provenance | Src:MaD:1 MaD:7 |
+| EmailBad.go:9:10:9:17 | selection of Header | EmailBad.go:9:10:9:29 | call to Get | provenance | Src:MaD:1 MaD:8 |
 | EmailBad.go:9:10:9:29 | call to Get | EmailBad.go:12:56:12:67 | type conversion | provenance |  |
 | main.go:31:21:31:31 | call to Referer | main.go:33:57:33:78 | type conversion | provenance | Src:MaD:2  |
+| main.go:39:21:39:31 | call to Referer | main.go:43:25:43:38 | untrustedInput | provenance | Src:MaD:2  |
+| main.go:43:25:43:38 | untrustedInput | main.go:43:18:43:22 | write [postupdate] | provenance | MaD:5 |
 | main.go:48:21:48:31 | call to Referer | main.go:54:46:54:59 | untrustedInput | provenance | Src:MaD:2  |
 | main.go:48:21:48:31 | call to Referer | main.go:55:52:55:65 | untrustedInput | provenance | Src:MaD:2  |
 | main.go:60:21:60:31 | call to Referer | main.go:62:47:62:60 | untrustedInput | provenance | Src:MaD:2  |
@@ -32,7 +37,7 @@ edges
 | main.go:113:21:113:31 | call to Referer | main.go:119:28:119:41 | untrustedInput | provenance | Src:MaD:2  |
 | main.go:116:29:116:30 | &... [postupdate] | main.go:124:57:124:57 | b | provenance |  |
 | main.go:119:3:119:4 | mw [postupdate] | main.go:116:29:116:30 | &... [postupdate] | provenance | FunctionModel |
-| main.go:119:28:119:41 | untrustedInput | main.go:119:3:119:4 | mw [postupdate] | provenance | MaD:6 |
+| main.go:119:28:119:41 | untrustedInput | main.go:119:3:119:4 | mw [postupdate] | provenance | MaD:7 |
 | main.go:124:57:124:57 | b | main.go:124:57:124:65 | call to Bytes | provenance | MaD:3 |
 | main.go:129:21:129:31 | call to Referer | main.go:136:30:136:43 | untrustedInput | provenance | Src:MaD:2  |
 | main.go:132:29:132:30 | &... [postupdate] | main.go:141:57:141:57 | b | provenance |  |
@@ -40,20 +45,28 @@ edges
 | main.go:136:18:136:27 | formWriter [postupdate] | main.go:135:20:135:21 | mw [postupdate] | provenance | FunctionModel |
 | main.go:136:30:136:43 | untrustedInput | main.go:136:18:136:27 | formWriter [postupdate] | provenance | MaD:5 |
 | main.go:141:57:141:57 | b | main.go:141:57:141:65 | call to Bytes | provenance | MaD:3 |
+| main.go:146:22:146:32 | call to Referer | main.go:151:11:151:33 | type conversion | provenance | Src:MaD:2  |
+| main.go:147:22:147:32 | call to Referer | main.go:152:11:152:33 | type conversion | provenance | Src:MaD:2  |
+| main.go:151:11:151:33 | type conversion | main.go:151:3:151:3 | w [postupdate] | provenance | MaD:6 |
+| main.go:152:11:152:33 | type conversion | main.go:152:3:152:3 | w [postupdate] | provenance | MaD:6 |
 models
 | 1 | Source: net/http; Request; true; Header; ; ; ; remote; manual |
 | 2 | Source: net/http; Request; true; Referer; ; ; ReturnValue; remote; manual |
 | 3 | Summary: bytes; Buffer; true; Bytes; ; ; Argument[receiver]; ReturnValue; taint; manual |
 | 4 | Summary: github.com/sendgrid/sendgrid-go/helpers/mail; ; false; NewContent; ; ; Argument[1]; ReturnValue; taint; manual |
 | 5 | Summary: io; ; false; WriteString; ; ; Argument[1]; Argument[0]; taint; manual |
-| 6 | Summary: mime/multipart; Writer; true; WriteField; ; ; Argument[0..1]; Argument[receiver]; taint; manual |
-| 7 | Summary: net/http; Header; true; Get; ; ; Argument[receiver]; ReturnValue; taint; manual |
+| 6 | Summary: io; Writer; true; Write; ; ; Argument[0]; Argument[receiver]; taint; manual |
+| 7 | Summary: mime/multipart; Writer; true; WriteField; ; ; Argument[0..1]; Argument[receiver]; taint; manual |
+| 8 | Summary: net/http; Header; true; Get; ; ; Argument[receiver]; ReturnValue; taint; manual |
 nodes
 | EmailBad.go:9:10:9:17 | selection of Header | semmle.label | selection of Header |
 | EmailBad.go:9:10:9:29 | call to Get | semmle.label | call to Get |
 | EmailBad.go:12:56:12:67 | type conversion | semmle.label | type conversion |
 | main.go:31:21:31:31 | call to Referer | semmle.label | call to Referer |
 | main.go:33:57:33:78 | type conversion | semmle.label | type conversion |
+| main.go:39:21:39:31 | call to Referer | semmle.label | call to Referer |
+| main.go:43:18:43:22 | write [postupdate] | semmle.label | write [postupdate] |
+| main.go:43:25:43:38 | untrustedInput | semmle.label | untrustedInput |
 | main.go:48:21:48:31 | call to Referer | semmle.label | call to Referer |
 | main.go:54:46:54:59 | untrustedInput | semmle.label | untrustedInput |
 | main.go:55:52:55:65 | untrustedInput | semmle.label | untrustedInput |
@@ -85,7 +98,10 @@ nodes
 | main.go:136:30:136:43 | untrustedInput | semmle.label | untrustedInput |
 | main.go:141:57:141:57 | b | semmle.label | b |
 | main.go:141:57:141:65 | call to Bytes | semmle.label | call to Bytes |
+| main.go:146:22:146:32 | call to Referer | semmle.label | call to Referer |
+| main.go:147:22:147:32 | call to Referer | semmle.label | call to Referer |
+| main.go:151:3:151:3 | w [postupdate] | semmle.label | w [postupdate] |
+| main.go:151:11:151:33 | type conversion | semmle.label | type conversion |
+| main.go:152:3:152:3 | w [postupdate] | semmle.label | w [postupdate] |
+| main.go:152:11:152:33 | type conversion | semmle.label | type conversion |
 subpaths
-testFailures
-| main.go:39:33:39:43 | comment | Missing result: Source |
-| main.go:42:24:42:33 | comment | Missing result: Alert |
diff --git a/go/ql/test/query-tests/Security/CWE-640/main.go b/go/ql/test/query-tests/Security/CWE-640/main.go
index f83b413ebc4..73ff8f6b1fb 100644
--- a/go/ql/test/query-tests/Security/CWE-640/main.go
+++ b/go/ql/test/query-tests/Security/CWE-640/main.go
@@ -39,8 +39,8 @@ func main() {
 		untrustedInput := r.Referer() // $ Source
 
 		s, _ := smtp.Dial("test.test")
-		write, _ := s.Data() // $ Alert
-		io.WriteString(write, untrustedInput)
+		write, _ := s.Data()
+		io.WriteString(write, untrustedInput) // $ Alert
 	})
 
 	// Not OK
@@ -141,6 +141,19 @@ func main() {
 		smtp.SendMail("test.test", nil, "from@from.com", nil, b.Bytes()) // $ Alert
 	})
 
+	// Not OK - check only one result when sink is Client.Data() from net/smtp
+	{
+		untrustedInput1 := r.Referer() // $ Source=s1
+		untrustedInput2 := r.Referer() // $ Source=s2
+		c, _ := smtp.Dial("mail.example.com:smtp")
+		w, _ := c.Data()
+		w.Write([]byte("safe text"))
+		w.Write([]byte(untrustedInput1)) // $ Alert=s1
+		w.Write([]byte(untrustedInput2)) // $ Alert=s2
+		w.Close()
+		c.Quit()
+	}
+
 	log.Println(http.ListenAndServe(":80", nil))
 
 }