Every guide sits in one of seven technical clusters. Start from the layer you are operating, or open the full guide index.
8 guides
Warmup is a way to build a recent, gradual sending pattern while authentication, bounces and real replies stay observable. These field notes cover mailbox warmup versus domain warmup, when to hold a ramp, how to move onto real prospect traffic without a cliff, and why a warmed mailbox can still land in spam.
Open Warmup & ramping →23 guides
Sender authentication is three separate mechanisms: SPF authorizes sending IPs, DKIM signs the message, and DMARC tests alignment between them and the visible From domain. These notes trace real failures — SPF PermError and the 10-lookup limit, DKIM selector and body-hash problems, and the 2026 RFC 9989 changes to DMARC — back to the standard that governs them.
Open SPF / DKIM / DMARC →8 guides
There is no universal safe number of cold emails per day. What you can control is the size of each change. These notes cover starting volume for a new domain, gating increases on evidence from the previous batch, tracking per-mailbox and per-domain totals together, and recovering after an accidental spike.
Open Sending volume →15 guides
Verification is several different checks — syntax, domain, MX, mailbox and suppression — and they can legitimately disagree. These notes cover catch-all domains, role addresses, re-verifying an old list, global hard-bounce suppression, deduplication across mailboxes, and the DNS edge cases (Null MX, NXDOMAIN, SERVFAIL) a verifier should never collapse into one result.
Open List hygiene →20 guides
Reply detection and mailbox cleanup run on IMAP, and IMAP has sharp edges: UIDs versus sequence numbers, UIDVALIDITY resets, folder-name and delimiter differences across providers, and IDLE reconnects that drop replies. These notes show how to read mail without marking it seen and how to build automation that degrades safely.
Open IMAP operations →13 guides
A follow-up system has to space touches sensibly and, more importantly, stop the moment a prospect replies — including from a different alias, or in the race between a locked job and the provider call. These notes also cover business-day scheduling, out-of-office handling, and RFC 8058 one-click unsubscribe.
Open Follow-up systems →15 guides
Recovery starts with noticing damage early and isolating one cause at a time. These notes cover triaging a bounce spike, responding to a complaint signal, pause-versus-reduce decisions, restarting after a quiet period, and reading specific Gmail, Yahoo and Outlook deferral and rejection codes.
Open Reputation recovery →