From 57729484f70a73b1de2399b61d78bb6c302e0bd9 Mon Sep 17 00:00:00 2001
From: Drew Smirnoff <me@andrinoff.com>
Date: Sat, 3 Jan 2026 18:38:34 +0400
Subject: [PATCH] fix(sender): encode the files sent from matcha (#84)

---
 sender/sender.go | 23 +++++++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)

diff --git a/sender/sender.go b/sender/sender.go
index bfd419199a286941e57f28485ed243466466cbae..aa7c6a41dec437fce1a74f336863d4e64552df23 100644
--- a/sender/sender.go
+++ b/sender/sender.go
@@ -127,7 +127,8 @@ func SendEmail(account *config.Account, to []string, subject, plainBody, htmlBod
 		if err != nil {
 			return err
 		}
-		imgPart.Write(data) // data is already base64 encoded
+		// data is already base64 encoded, but needs MIME line wrapping (76 chars per line)
+		imgPart.Write([]byte(wrapBase64(string(data))))
 	}
 
 	relatedWriter.Close() // Finish the related part
@@ -149,7 +150,8 @@ func SendEmail(account *config.Account, to []string, subject, plainBody, htmlBod
 			return err
 		}
 		encodedData := base64.StdEncoding.EncodeToString(data)
-		attachmentPart.Write([]byte(encodedData))
+		// MIME requires base64 to be line-wrapped at 76 characters
+		attachmentPart.Write([]byte(wrapBase64(encodedData)))
 	}
 
 	mainWriter.Close() // Finish the main message
@@ -157,3 +159,20 @@ func SendEmail(account *config.Account, to []string, subject, plainBody, htmlBod
 	addr := fmt.Sprintf("%s:%d", smtpServer, smtpPort)
 	return smtp.SendMail(addr, auth, account.Email, to, msg.Bytes())
 }
+
+// wrapBase64 wraps base64-encoded data at 76 characters per line as required by MIME.
+func wrapBase64(data string) string {
+	const lineLength = 76
+	var result strings.Builder
+	for i := 0; i < len(data); i += lineLength {
+		end := i + lineLength
+		if end > len(data) {
+			end = len(data)
+		}
+		result.WriteString(data[i:end])
+		if end < len(data) {
+			result.WriteString("\r\n")
+		}
+	}
+	return result.String()
+}