darkzwarmer vs MailStrike

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.

MailStrike is an email deliverability platform for mailbox warming, placement testing, and seed lists for B2C senders. AI personas create and reply to email threads using a company's description and industry. Its warming network exchanges threads among business mailboxes while excluding spammers, free-mail senders, and dodgy sites. On connection, the service checks SPF, DKIM, DMARC, and MX records and identifies missing values. Google Workspace and Microsoft 365 connect through OAuth; other providers use IMAP and SMTP with an app password. Warming reaches full volume by day 21 and then continues at a maintenance volume. Seed lists monitor placement and can interact with messages; setup requires one DNS TXT record for domain verification. A free deliverability test reports inbox, promotions, or spam placement and scores spam signals without requiring a card. MailStrike runs on the web and through an API. Paid plans start at $18/mo (annual); there is no free plan, but a free trial is available.