darkzwarmer vs WarmEnvelopes

darkzwarmer is an open-source email warmup tool for domains and mailboxes the user owns and controls. It generates inboxes across those domains, exchanges warmup mail only between different domains, and replies to its own network’s messages after random delays of 30 minutes to four hours; messages from outsiders are ignored. Per-inbox volume rises from 5 to 35 messages daily over 28 days, then stays at the chosen steady-state level. Sends are randomized across a default 07:00–19:00 local window, with 2–8 minutes of jitter between consecutive sends; weekends pause. Outbound mail uses configurable SMTP, with Amazon SES, SMTP.com, Postmark, Mailgun, Brevo and SendGrid listed as examples. Inbound mail can use IMAP or Resend. The Python 3.11+ runtime stores state in SQLite and is designed to resume after crashes or reboots while preventing duplicate replies. It requires an always-on machine, at least two user-owned domains, SMTP service and an inbound-mail route. Windows scripts support unattended operation; Linux and macOS users can run it under a process manager or terminal session. Configuration includes inbox counts, timing, volume limits and optional scheduled inbox cohorts. The project is MIT-licensed and provided without warranty.

WarmEnvelopes is a web service that schedules genuine warm-up emails from a configured domain through the user’s Resend account. Messages go to inboxes the user controls, or whose owners have consented, to build sending history. Setup requires a verified sending domain and a Resend API key, with a separate key stored for each domain. A scheduler runs every 30 minutes and spreads the daily target across the day. Pro users can set starting volume, daily increases, and a maximum. The library contains more than 1,000 independently written messages in several languages, varying templates and sender names. Each send records its sender, template, delivery status, and errors, while the dashboard shows daily progress. The Free plan costs 0.00 EUR and permits four emails per day per domain across up to 10 domains. Pro costs €9 a month and supports up to 1,000 daily emails. A separate checker reviews SPF, DKIM, DMARC, MX, and blocklist status.