darkzwarmer vs InboxPlan

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.

InboxPlan is a web service for automated email warm-up, scheduling, and deliverability monitoring. It creates warm-up messages and simulated two-way conversations tailored to a user's industry, then schedules activity with randomized send windows and a gradual increase in volume. InboxPlan says sending typically starts at 3–5 emails per day in week one and reaches 30–50 per day by week four; users can set manual limits for each account. A live monitor tracks sender score, inbox placement, and spam rates across major providers. Users can connect Gmail, Outlook, Zoho, or custom SMTP accounts and warm multiple mailboxes in one workspace, subject to the plan's account allowance. Each account receives its own threads, schedule, and reputation dashboard. InboxPlan says it uses OAuth and does not store account passwords. It names sales teams, agencies, and startups among its intended users, as well as businesses in SaaS, recruiting, real estate, finance, and e-commerce. The service is paid, with no free plan, and offers a 7-day free trial that requires a credit card. InboxPlan was founded in 2022 and is headquartered in San Francisco, California.