Engineering notes, policy decisions and sending guidance from the team building Warmbly.https://warmbly.com/en-ushttps://warmbly.com/blog/open-source-cold-email-platform/https://warmbly.com/blog/open-source-cold-email-platform/Warmbly is Apache 2.0 cold email plus warmup you can self-host. What running it yourself means for IPs, workers, and your data, and when cloud is the better call.Sat, 04 Jul 2026 00:00:00 GMThttps://warmbly.com/blog/how-many-cold-emails-per-day-per-mailbox/https://warmbly.com/blog/how-many-cold-emails-per-day-per-mailbox/The safe number is per mailbox, not per account: 50/day default, 100 hard max, a 600s gap between sends. Here is the math to plan any daily volume.Thu, 02 Jul 2026 00:00:00 GMThttps://warmbly.com/blog/how-email-warmup-actually-works/https://warmbly.com/blog/how-email-warmup-actually-works/Warmup ramps a mailbox from 10/day, +1/day, to a 40/day ceiling over a few weeks. Here is the real mechanism: pools, partner selection, tokens, and why we cap it.Tue, 30 Jun 2026 00:00:00 GMThttps://warmbly.com/blog/delivery-rate-is-not-inbox-placement/https://warmbly.com/blog/delivery-rate-is-not-inbox-placement/A 99% delivery rate can still mean the spam folder. What delivered actually means, why it is not placement, and how to tell where your cold email lands.Sat, 27 Jun 2026 00:00:00 GMThttps://warmbly.com/blog/spf-dkim-dmarc-alignment-cold-email/https://warmbly.com/blog/spf-dkim-dmarc-alignment-cold-email/SPF and DKIM can both pass while DMARC alignment quietly fails. How to read your Authentication-Results header and confirm the From domain actually aligns.Wed, 24 Jun 2026 00:00:00 GMThttps://warmbly.com/blog/how-many-mailboxes-and-domains-cold-email/https://warmbly.com/blog/how-many-mailboxes-and-domains-cold-email/Planning cold email volume comes down to per-mailbox budgets. Work backward from your daily target to the mailboxes, domains, and IP spread you actually need.Mon, 22 Jun 2026 00:00:00 GMThttps://warmbly.com/blog/getting-a-mailbox-back-into-warmup-pool/https://warmbly.com/blog/getting-a-mailbox-back-into-warmup-pool/A step-by-step recovery ramp for a mailbox that has been quarantined or blacklisted: confirm listings, stop the bleeding, fix the root cause, re-warm at 5 to 10/day.Fri, 19 Jun 2026 00:00:00 GMThttps://warmbly.com/blog/complaint-rate-that-gets-you-throttled/https://warmbly.com/blog/complaint-rate-that-gets-you-throttled/The numbers that actually trigger enforcement: Google spam under 0.10%, SES complaint under 0.1% and bounce under 5%. Plus the stricter bands we quarantine at.Tue, 16 Jun 2026 00:00:00 GMThttps://warmbly.com/blog/mailbox-budgets-not-server-settings/https://warmbly.com/blog/mailbox-budgets-not-server-settings/People keep asking us to raise their daily limit. The honest answer is that the limit they are asking about does not exist.Wed, 10 Jun 2026 00:00:00 GMThttps://warmbly.com/blog/quarantine-early/https://warmbly.com/blog/quarantine-early/Most warmup tools pull a mailbox at 80% spam placement. Warmbly quarantines at 20%, on separate signals with sample floors, and re-entry you have to earn.Tue, 09 Jun 2026 00:00:00 GMThttps://warmbly.com/blog/reading-the-bulk-sender-rules/https://warmbly.com/blog/reading-the-bulk-sender-rules/SPF, DKIM, DMARC alignment, one-click unsubscribe, spam under 0.10%: Google and Microsoft now enforce the same bulk bar. The checklist, and the two gotchas.Mon, 08 Jun 2026 00:00:00 GMT