darkzwarmer vs Inbox Warmup

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.

Inbox Warmup connects SMTP infrastructure, authenticates domains, warms sending activity, monitors reputation signals, manages replies, and controls campaigns from a web and API dashboard. It supports SMTP ports 465 with SSL/TLS, 587 with STARTTLS, and compatible custom ports. Checks include SPF, DKIM, DMARC, Return-Path, ownership, and tracking records. Warm-up automation increases activity gradually, rotates sending, respects mailbox limits, and can pause when health signals need attention. Campaign tools provide templates, personalization, timezone scheduling, hourly and daily limits, and pause or resume controls. Listed mailbox providers include Gmail, Workspace, Outlook, Yahoo, and IMAP accounts, with Google Postmaster and Yahoo sender-data integrations. Launch costs $39 a month after a $1 first seven days; Growth is $99 a month and Professional $199 a month on the same terms. Agency pricing is custom. Credits reset monthly and do not roll over.