darkzwarmer vs SendScale Email 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.

SendScale Email Warmup is a service for warming email accounts and building sender reputation for cold outreach. It connects Google Workspace and Microsoft 365 inboxes through OAuth, then uses AI to exchange unique messages between accounts in a private network SendScale says contains more than one million inboxes. The service says its system opens and scrolls through messages and replies in human-style language. If a warmup email lands in spam, SendScale says it moves the message out, marks it important, and replies. A dashboard tracks daily sends and replies, spam-versus-inbox placement trends, and readiness. SendScale recommends 14 days for new domains and says the dashboard indicates when warmup is complete; warmup can continue at lower volume while campaigns run. The service also describes account rotation for load balancing and a Master Smartbox for consolidating replies. Its free plan includes pre-warmed inboxes, warmup tools, in-product conversational guidance, and campaign access. Paid plans start at $28/mo billed annually. The privacy policy places database servers exclusively in the European Union and describes industry-standard security measures.