Start (sender/sender.go)

Module exposing: Start, Next, smimeOuterBoundary, smtpHelloHostname, extractBareEmail, generateMessageID, containsMarkup, detectPlaintextOnly

// Source: https://github.com/floatpane/matcha | License: MIT | Copyright 2026 floatpane
// Provided via justclaw.it.com; keep this notice with the code.
package sender

import (
	"bytes"
	"context"
	"crypto/rand"
	"crypto/tls"
	"crypto/x509"
	"encoding/base64"
	"encoding/pem"
	"errors"
	"fmt"
	"io"
	"mime"
	"mime/multipart"
	"mime/quotedprintable"
	"net"
	"net/mail"
	"net/smtp"
	"net/textproto"
	"os"
	"path/filepath"
	"strings"
	"time"

	"github.com/ProtonMail/go-crypto/openpgp"
	messagetextproto "github.com/emersion/go-message/textproto"
	"github.com/emersion/go-pgpmail"
	"github.com/floatpane/matcha/clib"
	"github.com/floatpane/matcha/config"
	"github.com/floatpane/matcha/internal/httpclient"
	"github.com/floatpane/matcha/internal/loglevel"
	"github.com/floatpane/matcha/pgp"
	"github.co

... (truncated -- full source via MCP)