fix(gmail): stop hard-wrapping plain text email bodies at ~72 chars

internal/cmd/gmail_mime.go

@@ -7,6 +7,7 @@ import (
 	"errors"
 	"fmt"
 	"mime"
+	"mime/quotedprintable"
 	"net/mail"
 	"net/url"
 	"os"
@@ -142,9 +143,9 @@ func buildRFC822(opts mailOptions, cfg *rfc822Config) ([]byte, error) {
 			return b.Bytes(), nil
 		default:
 			writeHeader(&b, "Content-Type", "text/plain; charset=\"utf-8\"")
-			writeHeader(&b, "Content-Transfer-Encoding", "7bit")
+			writeHeader(&b, "Content-Transfer-Encoding", "quoted-printable")
 			b.WriteString("\r\n")
-			writeBodyWithTrailingCRLF(&b, plainBody)
+			writeQuotedPrintableBody(&b, plainBody)
 			return b.Bytes(), nil
 		}
 	}
@@ -175,8 +176,8 @@ func buildRFC822(opts mailOptions, cfg *rfc822Config) ([]byte, error) {
 		writeBodyWithTrailingCRLF(&b, htmlBody)
 	default:
 		b.WriteString("Content-Type: text/plain; charset=\"utf-8\"\r\n")
-		b.WriteString("Content-Transfer-Encoding: 7bit\r\n\r\n")
-		writeBodyWithTrailingCRLF(&b, plainBody)
+		b.WriteString("Content-Transfer-Encoding: quoted-printable\r\n\r\n")
+		writeQuotedPrintableBody(&b, plainBody)
 	}
 
 	// Attachments
@@ -282,6 +283,16 @@ func wrapBase64(b []byte) string {
 	return out.String()
 }
 
+func writeQuotedPrintableBody(b *bytes.Buffer, body string) {
+	qpw := quotedprintable.NewWriter(b)
+	_, _ = qpw.Write([]byte(body))
+	_ = qpw.Close()
+	// Ensure trailing CRLF after the encoded body.
+	if !bytes.HasSuffix(b.Bytes(), []byte("\r\n")) {
+		b.WriteString("\r\n")
+	}
+}
+
 func writeBodyWithTrailingCRLF(b *bytes.Buffer, body string) {
 	b.WriteString(body)
 	if !strings.HasSuffix(body, "\r\n") {
@@ -292,8 +303,13 @@ func writeBodyWithTrailingCRLF(b *bytes.Buffer, body string) {
 func writeTextPart(b *bytes.Buffer, boundary string, contentType string, body string) {
 	_, _ = fmt.Fprintf(b, "--%s\r\n", boundary)
 	_, _ = fmt.Fprintf(b, "Content-Type: %s\r\n", contentType)
-	b.WriteString("Content-Transfer-Encoding: 7bit\r\n\r\n")
-	writeBodyWithTrailingCRLF(b, body)
+	if strings.HasPrefix(contentType, "text/plain") {
+		b.WriteString("Content-Transfer-Encoding: quoted-printable\r\n\r\n")
+		writeQuotedPrintableBody(b, body)
+	} else {
+		b.WriteString("Content-Transfer-Encoding: 7bit\r\n\r\n")
+		writeBodyWithTrailingCRLF(b, body)
+	}
 }
 
 func randomBoundary() (string, error) {

internal/cmd/gmail_mime_test.go

@@ -1,6 +1,8 @@
 package cmd
 
 import (
+	"io"
+	"mime/quotedprintable"
 	"regexp"
 	"strings"
 	"testing"
@@ -342,6 +344,86 @@ func TestFormatAddressHeadersFiltersEmpty(t *testing.T) {
 	}
 }
 
+func TestBuildRFC822PlainBodyNotHardWrapped(t *testing.T) {
+	// A single long paragraph (~200 chars) must survive round-trip through
+	// quoted-printable encoding without hard line breaks in the decoded output.
+	longLine := "Hope you are doing well. I wanted to connect you both as I believe there could be a mutually interesting conversation around potential synergies between your respective companies and their product offerings."
+	raw, err := buildRFC822(mailOptions{
+		From:    "a@b.com",
+		To:      []string{"c@d.com"},
+		Subject: "Test",
+		Body:    longLine,
+	}, nil)
+	if err != nil {
+		t.Fatalf("err: %v", err)
+	}
+	s := string(raw)
+
+	// Must use quoted-printable, not 7bit, to avoid transport-level wrapping.
+	if !strings.Contains(s, "Content-Transfer-Encoding: quoted-printable") {
+		t.Fatalf("expected quoted-printable encoding, got: %q", s)
+	}
+
+	// Decode the QP body and verify the original line is intact.
+	// Split at the header/body separator.
+	parts := strings.SplitN(s, "\r\n\r\n", 2)
+	if len(parts) != 2 {
+		t.Fatalf("could not find header/body separator in: %q", s)
+	}
+	bodyEncoded := parts[1]
+	decoded, err := io.ReadAll(quotedprintable.NewReader(strings.NewReader(bodyEncoded)))
+	if err != nil {
+		t.Fatalf("QP decode error: %v", err)
+	}
+	decodedStr := strings.TrimRight(string(decoded), "\r\n")
+	if decodedStr != longLine {
+		t.Fatalf("decoded body mismatch:\n  got:  %q\n  want: %q", decodedStr, longLine)
+	}
+}
+
+func TestBuildRFC822PlainBodyMultiParagraph(t *testing.T) {
+	body := "First long paragraph that should flow naturally without any hard wrapping at seventy-two characters or any other artificial limit.\r\n\r\nSecond paragraph also long enough to verify it stays as one logical line when decoded from quoted-printable.\r\n\r\nThird short paragraph."
+	raw, err := buildRFC822(mailOptions{
+		From:    "a@b.com",
+		To:      []string{"c@d.com"},
+		Subject: "Test",
+		Body:    body,
+	}, nil)
+	if err != nil {
+		t.Fatalf("err: %v", err)
+	}
+	s := string(raw)
+
+	parts := strings.SplitN(s, "\r\n\r\n", 2)
+	if len(parts) != 2 {
+		t.Fatalf("could not find header/body separator")
+	}
+	decoded, err := io.ReadAll(quotedprintable.NewReader(strings.NewReader(parts[1])))
+	if err != nil {
+		t.Fatalf("QP decode error: %v", err)
+	}
+	decodedStr := strings.TrimRight(string(decoded), "\r\n")
+	if decodedStr != body {
+		t.Fatalf("decoded body mismatch:\n  got:  %q\n  want: %q", decodedStr, body)
+	}
+}
+
+func TestBuildRFC822HTMLBodyStays7bit(t *testing.T) {
+	raw, err := buildRFC822(mailOptions{
+		From:     "a@b.com",
+		To:       []string{"c@d.com"},
+		Subject:  "Test",
+		BodyHTML: "<p>Hello world</p>",
+	}, nil)
+	if err != nil {
+		t.Fatalf("err: %v", err)
+	}
+	s := string(raw)
+	if !strings.Contains(s, "Content-Transfer-Encoding: 7bit") {
+		t.Fatalf("expected 7bit encoding for HTML body, got: %q", s)
+	}
+}
+
 func TestFormatAddressHeadersParsesCommaSeparatedList(t *testing.T) {
 	got := formatAddressHeaders([]string{"Alice <a@b.com>, Bob <b@c.com>"})
 	parts := strings.SplitN(got, ", ", 2)