darkzwarmer vs EmailWarmup

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.

EmailWarmup is a web and API service that uses AI-generated conversations and automated engagement to warm mailboxes for cold-email sending. Connected mailboxes pair in both directions with active peers, exchanging messages inside the network. AI creates subjects and replies with changing topics and tones, retaining a [WARMUP] subject tag. Slow, medium, and fast schedules gradually raise sending volume over several days. Supported engagement includes threaded replies, reads, stars, spam-folder rescue, and delivery checks. Gmail connects through OAuth, while SMTP/IMAP credentials are also supported; the maker says credentials are encrypted at rest and personal email content is not read or stored. Account data is retained while an account is active and deleted within 30 days after account deletion. A free Community plan lists one mailbox and 10 warmup emails per day. Paid plans start with Starter at $19 a month; Growth is $49 a month and Agency is $149 a month. EmailWarmup does not send outreach campaigns, repair blocklisted domains, or guarantee inbox placement.