Lemlist

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Build me cold outreach that replaces Lemlist — and read this before deciding, because two things here deserve more scepticism than usual.

The technical answer is that **a warm-up network needs many participants to work at all**, and you cannot have one alone. The other answer is that this category is where mass unsolicited email comes from, and in most of Europe sending it to individuals without consent is unlawful. Build this for follow-up to people who asked, for reply-tracked sequences to existing contacts, or for business-to-business outreach where you have checked the rules where the recipient lives. Do not build a spam cannon; it will destroy the sending domain you actually need.

STACK
- Node 20+ with Fastify, server-rendered HTML
- SQLite through better-sqlite3, WAL mode
- Sending through your own mailbox over the provider's API or SMTP, not through a bulk platform
- A worker for sending, separate from the web process
- Caddy in front

THE DATA MODEL
- mailboxes: id, address, provider, credentials_encrypted, daily_limit, sent_today, warmup_state, health_json, is_active
- contacts: id, email, name, company, attributes_json, status, source, consent_basis, do_not_contact, created_at
- sequences: id, name, steps_json, stop_on_reply, stop_on_click, sending_window_json, timezone_mode, is_active
- enrolments: id, sequence_id, contact_id, mailbox_id, status, current_step, next_send_at, started_at, stopped_at, stop_reason
- sends: id, enrolment_id, step_index, mailbox_id, message_id, thread_id, sent_at, opened_at, replied_at, bounced_at, error
- replies: id, send_id, received_at, is_auto_reply, classification
- suppression: email_hash, domain, reason, at — global, permanent

SENDING FROM A REAL MAILBOX
- One mailbox sends a modest number a day. Fifty is careful, a couple of hundred is aggressive, and going higher is what gets an account restricted
- Randomised intervals within a sending window in the recipient's own working hours. A message every twelve seconds exactly is a machine and every provider knows it
- Rotate across mailboxes if you have several, each with its own limit and its own health
- Sends as replies within a thread for follow-ups, with the correct headers, because that is how a sequence reads as a conversation rather than a campaign
- Track the mailbox's own bounce and complaint signals and stop that mailbox automatically when they rise. One bad list can cost you the address you actually use for work

STOPPING, WHICH IS THE MOST IMPORTANT PART
- A reply stops the sequence immediately. Detect it by thread and by Message-ID references, and classify automatic replies so an out-of-office does not count
- A bounce stops it and suppresses the address
- An unsubscribe stops it everywhere, permanently, and every message carries a one-click way out even though it is not a marketing platform — because it is the decent thing and it keeps you out of trouble
- A manual do-not-contact list, by address and by domain, checked before every send
- Any doubt about whether somebody wants this stops the sequence. The whole reputational risk of this category is in the fourth message to somebody who ignored the first three

PERSONALISATION, HONESTLY
- Variables with a fallback, so nobody receives 'Hi ,' or 'I noticed your work at .'
- A required review of the first send of every sequence, rendered for a real contact
- Personalised images and dynamic landing pages exist and are mostly a gimmick that raises the spam score. Plain text from a real mailbox outperforms them, and it is also what a person would actually send

WARM-UP, HONESTLY
- The network effect is unreproducible alone. What you can do: send gradually increasing volume to addresses that genuinely engage, keep the list clean, and be patient for weeks
- Set up SPF, DKIM and DMARC properly, use a subdomain separate from anything else, and monitor the postmaster reports the large providers offer

MEASURING
- Sent, delivered, opened, replied, bounced, unsubscribed, per sequence and per step
- Reply rate is the only number that matters. Open rate is unreliable and click tracking in a one-to-one email raises the spam score — consider leaving it off entirely

OPERATIONS
- .env: DATABASE_PATH, BASE_URL, ENCRYPTION_KEY, SESSION_SECRET, HASH_SALT, provider credentials
- Migrations on boot, each once; nightly backup off the machine
- Health endpoint reporting per-mailbox bounce rate and daily volume

WHAT MATTERS MOST
Reply detection and the stop rules. Build those before the first sequence runs, and keep the volume low — the mailbox you are risking is the one you use for everything else.