darkzwarmer vs WarmupHero

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.

WarmupHero is an email warmup service that gradually increases sending volume to build an address’s reputation and reduce spam risk. It says setup takes one minute, works with all email service providers and runs automatically. The service exchanges warm-up messages with real people, sends personalized emails sequentially and keeps messages in conversation threads with automated replies. It opens warm-up emails, marks them important and moves them back to the inbox when they land in spam. Analytics show whether messages reach the inbox, spam or folders such as Promotions and Updates. Users can customize messages and add signatures containing images or links. Connections include the Office365 API and an SMTP/IMAP method for other business accounts. SmartReach.io users generate an API key before connecting an email account. WarmupHero is available as a web service and extension, with spam monitoring listed. Its free SmartReach.io plan costs nothing. The privacy policy says it does not access, read or delete users’ emails, while it may process information supplied about recipients and customers.