darkzwarmer vs Mailwarmup

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.

Mailwarmup is a web service that aims to raise sender reputation by generating positive email engagement through a shared network of more than 10,000 inboxes. After users connect an account using SMTP and IMAP details, it sends scheduled messages on their behalf. Network inboxes open and reply to messages, mark them important, and remove them from spam. A dashboard tracks warmup results, including messages removed from spam, categories, and email deliverability. Listed integrations include Gmail, Outlook, and SMTP; users can control sending and limits. Other listed tools include a Mail Health Score, blacklist monitoring, delivery statistics, blacklist removal prompts, and AI ramp ups in beta. Warmup messages can be filtered into a separate folder using the subject keyword “WUA.” There is no free plan, but a 7-day trial is offered. Starter costs $19 a month for one email account and up to 50 positive engagements per day. Growth is $49 a month for three accounts and up to 50 engagements daily; Scale is $99 a month for eight accounts and up to 100 daily; Powerhouse is $149 a month for eight accounts and up to 300 daily. Warmup does not guarantee inbox placement.