Email infrastructure and deliverability
Configuring domains, subdomains and inboxes to maintain sender reputation and inbox placement. Every Cold Email Daily story on email infrastructure and deliverability, newest first. 30 stories since September 2026.
- Christian maps 12 stages to becoming a GTM engineer
The path starts at secondary domains and ends at context files, and the testing stage decides who can actually run it.
- Nowoslawski says .pro and .info still send fine
The reseller versus manual comparison ended level, and the follow-up question was which cheap domains still land.
- Illingworth says a client went 68 days without inbox checks
The vendor's own numbers on automated inbox monitoring, including 12,817 blocked dead addresses.
- Haren says Azure inboxes are getting cooked
The $1 mailbox sits inside someone else's tenant, and Microsoft punishes the whole tenant at once.
- Illingworth puts a lifespan cost on every extra daily send
His fix when a campaign needs more volume is more inboxes, not a higher daily number.
Know what is landing before you burn another domain
One email a day. Under three minutes. What the operators found out yesterday.
- Illingworth, rebuild a domain 3 times before buying a new one
The domain-level version of his lifespan play, built on a book of 570,000+ inboxes he says his team has set up.
- Shields posts a 60-day plan to rebuild to $20k a month
The arithmetic rests on a single ratio from his own sending, and the post ends with a link to book a call with him.
- Haren says he lost 31,000 inboxes in a single day
The burn numbers behind his switch to a human copywriter and one send day per week.
- Abraham says reseller domain markup cost him up to $40K
He only caught it when infra spend climbed on his P&L while sending capacity stayed flat.
- Illingworth posts the subdomain rules behind 60 inboxes per domain
A root that never sends, 20 branches maximum, and a warning that none of it pays off at 30 inboxes.
- Illingworth says 60 inboxes need $10 of domains, not $200
He says he tested the belief that subdomains on one root all burn together and found no deliverability difference.
- Illingworth says a reply rate drop rarely needs new domains
His checklist reads drift at domain level, tests with a bland email, then rebuilds accounts in a new Google admin panel to pick up a different IP.
- Illingworth says parallel warmup doubled his inbox lifespan
One operator's replacement cycle, with 10 cold and 20 warmup emails a day per inbox and no placement test attached.
- Haren defends his 4x infra multiplier, Mars calls it insurance on insurance
The dispute over a 10 cent per email infrastructure figure comes down to how much redundancy you buy before you send.
- Illingworth posts the six sending rules behind his agency
Twenty sends per inbox, three inboxes per domain, 14 days of warmup and a 70% health score before anything goes out.
- Haren, a typo across 34 warmed domains nearly sank his agency
The spare set of warmed infrastructure is the part worth copying, not the ARR number attached to the story.
- Luckforest hit 0 of 12 Outlook inboxes with auth passing
A placement test found Gmail fine and Outlook junking everything, on a list that was 44% Outlook.
- Haren now sends cold email formatted like marketing email
One sender's switch, built on a briefing from a provider he says pushes over a trillion emails a week.
- Christian says he monitored 75,235 inboxes
The post carries a count and a link, and nothing anyone else can check against.
- Illingworth says subdomains held across 1.8M sends
A client ran 5,000 Google accounts on 10 subdomains per root, and Illingworth says the root never sent a single cold email.
- Feldman's rebuilt dental campaign hits 0.733% qualified interest
Over half the replies on the original run were out-of-office autoresponders, and rescoring flipped which angle won.
- Illingworth and Shields put replies upstream of copy
Two senders spent the week arguing that inbox placement is arithmetic, not writing.
- Illingworth gives away an infrastructure spec for 10,000 sends a day
A free blueprint with a sizing formula, a four week warmup schedule and a bounce rate target, and no reply numbers behind it.
- Shields caps inboxes at 20 sends, runs 120 for 2,400 a day
A client asked why he could not just send from his own Gmail, and Shields published the arithmetic.
- Christian splits cold email sends by MX record
One enrichment column, two campaigns, and a reply rate that finally means something.
- Abraham posts a three-step test for copy versus infra
The test isolates one variable before you tear down a sending setup that may be fine.
- Illingworth says campaigns held with almost no warmup
One operator, no send volumes posted, and he says he is still testing.
- Illingworth says config rebuild took a client 0.9% to 23% replies
One operator's before and after, with the copy and the list held constant.
- Berman says spam filters ignore your subject line
A six item checklist posted with no data behind it, and copy comes last on the list.
- Illingworth says one $10 domain can carry 60 inboxes
The spec sits behind a comment gate, and the same operator lists 10 inboxes on one domain as a spam cause.
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Cold email and outbound, read daily so you do not have to. The campaigns, the reply rates, the deliverability findings and the copy that ran, from operators who send at real volume. No revenue flexes, no course launches.