diff --git a/internal/email/email.go b/internal/email/email.go
index 383045e..27048ee 100644
--- a/internal/email/email.go
+++ b/internal/email/email.go
@@ -4,6 +4,7 @@ package email
 
 import (
 	"fmt"
+	"os"
 	"time"
 
 	"github.com/wneessen/go-mail"
@@ -85,7 +86,32 @@ func SendFiles(cfg Config, to, subject, body string, attachPaths []string) error
 		return fmt.Errorf("smtp client: %w", err)
 	}
 	if err := client.DialAndSend(m); err != nil {
-		return fmt.Errorf("send: %w", err)
+		return fmt.Errorf("send via %s:%d (%s, %s): %w",
+			cfg.Host, cfg.Port, cfg.Encryption, describeSize(attachPaths), err)
 	}
 	return nil
 }
+
+// describeSize reports what was attached, in bytes.
+//
+// "An existing connection was forcibly closed" during DATA is the same message
+// whether the server refused the size, hit a quota, or simply dropped the
+// socket — and the first of those is the only one the operator can act on
+// directly. Naming the size rules it in or out without a second attempt.
+func describeSize(paths []string) string {
+	var total int64
+	n := 0
+	for _, p := range paths {
+		if p == "" {
+			continue
+		}
+		if fi, err := os.Stat(p); err == nil {
+			total += fi.Size()
+			n++
+		}
+	}
+	if n == 0 {
+		return "no attachment"
+	}
+	return fmt.Sprintf("%d attachment(s), %d KB", n, (total+1023)/1024)
+}
diff --git a/internal/email/size_test.go b/internal/email/size_test.go
new file mode 100644
index 0000000..37ba242
--- /dev/null
+++ b/internal/email/size_test.go
@@ -0,0 +1,34 @@
+package email
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+// "An existing connection was forcibly closed" during DATA reads the same
+// whether the server refused the SIZE, hit a quota, or just dropped the socket
+// — and only the first is something the operator can act on. Naming the size in
+// the error rules it in or out without a second attempt.
+func TestDescribeSize(t *testing.T) {
+	dir := t.TempDir()
+	a := filepath.Join(dir, "card.jpg")
+	if err := os.WriteFile(a, make([]byte, 2048), 0o644); err != nil {
+		t.Fatal(err)
+	}
+
+	if got := describeSize(nil); got != "no attachment" {
+		t.Errorf("no attachment = %q", got)
+	}
+	if got := describeSize([]string{""}); got != "no attachment" {
+		t.Errorf("blank path = %q, want it ignored", got)
+	}
+	if got := describeSize([]string{a}); got != "1 attachment(s), 2 KB" {
+		t.Errorf("one file = %q", got)
+	}
+	// A path that does not exist must not be counted — the mail library skips it,
+	// so reporting it would describe a message that was never sent.
+	if got := describeSize([]string{a, filepath.Join(dir, "gone.jpg")}); got != "1 attachment(s), 2 KB" {
+		t.Errorf("missing file counted: %q", got)
+	}
+}