feat(mail): save sent emails to the IMAP Sent folder

SMTP does not file a copy of outgoing mail, so append each sent message
to the Sent folder over IMAP (special-use \Sent, common names, else
create "Sent"). Best-effort: a failed copy is logged and never fails
the send.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/utils/mail.ts

@@ -1,4 +1,7 @@
 import nodemailer from 'nodemailer'
+import MailComposer from 'nodemailer/lib/mail-composer'
+import type Mail from 'nodemailer/lib/mailer'
+import { ImapFlow } from 'imapflow'
 
 const transporter = nodemailer.createTransport({
   host: process.env.SMTP_HOST,
@@ -9,23 +12,65 @@ const transporter = nodemailer.createTransport({
   }
 })
 
+const domain = () => (process.env.SMTP_FROM || '').match(/@([^>\s]+)/)?.[1] || 'preservetube.com'
+
+// smtp does not file a copy anywhere, so put it in the imap Sent folder ourselves
+async function saveToSent(options: Mail.Options) {
+  if (!process.env.IMAP_HOST || !process.env.IMAP_USER || !process.env.IMAP_PASS) return
+
+  const port = Number(process.env.IMAP_PORT || 993)
+  const client = new ImapFlow({
+    host: process.env.IMAP_HOST,
+    port,
+    secure: port === 993,
+    auth: { user: process.env.IMAP_USER, pass: process.env.IMAP_PASS },
+    logger: false
+  })
+  client.on('error', (error: Error) => console.log(`[mail] imap connection error: ${error.message}`))
+
+  try {
+    const raw = await new MailComposer(options).compile().build()
+    await client.connect()
+
+    const boxes = await client.list()
+    const sent = boxes.find(box => box.specialUse === '\\Sent')?.path
+      || boxes.find(box => /^(inbox[./])?sent( items| messages)?$/i.test(box.path))?.path
+    let path = sent
+    if (!path) {
+      path = 'Sent'
+      await client.mailboxCreate(path).catch(() => {})
+    }
+
+    await client.append(path, raw, ['\\Seen'], options.date instanceof Date ? options.date : new Date())
+  } catch (error: unknown) {
+    // the mail itself already went out, a missing copy must never fail the caller
+    console.log(`[mail] could not save copy to Sent: ${(error as Error).message}`)
+  } finally {
+    await client.logout().catch(() => {})
+  }
+}
+
+async function sendMail(options: Mail.Options) {
+  const full: Mail.Options = { ...options, from: process.env.SMTP_FROM, date: new Date() }
+  await transporter.sendMail(full)
+  await saveToSent(full)
+}
+
 async function sendRestoreCompleteEmail(to: string, videoId: string, title?: string | null) {
   const watchUrl = `https://preservetube.com/watch?v=${videoId}`
 
-  await transporter.sendMail({
-    from: process.env.SMTP_FROM,
+  await sendMail({
     to,
     subject: 'Your PreserveTube video has been restored',
+    messageId: `<${crypto.randomUUID()}@${domain()}>`,
     text: `The video you requested${title ? ` ("${title}")` : ''} has been restored from cold storage and is available again:\n\n${watchUrl}`
   })
 }
 
 async function sendArchiveReplyEmail(to: string, subject: string, text: string, inReplyTo?: string) {
-  const domain = (process.env.SMTP_FROM || '').match(/@([^>\s]+)/)?.[1] || 'preservetube.com'
-  const messageId = `<${crypto.randomUUID()}@${domain}>`
+  const messageId = `<${crypto.randomUUID()}@${domain()}>`
 
-  await transporter.sendMail({
-    from: process.env.SMTP_FROM,
+  await sendMail({
     to,
     subject: /^re:/i.test(subject) ? subject : `Re: ${subject}`,
     text,