Notes from the deliverability lab.
Why 2-to-3 mailboxes per domain is the deliverability ceiling nobody tells you
Why InboxLee refuses to provision a fourth mailbox on a single domain, what the domain-level signal actually is, and how to plan a ramp around it.
The InboxLee TeamApr 22DKIM explained: what it is and why every cold sender needs it
What DKIM does, why 2048-bit, how propagation works, what InboxLee sets automatically.
The InboxLee TeamApr 20SPF, DKIM, and DMARC: the cold-email checklist Google actually checks in 2026
The three records every cold sender needs, what each one does, what Google and Microsoft penalise when they are wrong.
The InboxLee TeamApr 8DMARC p=quarantine vs p=reject: which one is right for cold email
Reject sounds stronger. Quarantine ships safer. Here is the operator-grade reasoning for picking the right policy.
The InboxLee TeamApr 7DKIM key rotation for cold email: when, why, and how often
Rotation is operational hygiene, not a security stunt. Here is the cadence that holds up under enterprise audits and Gmail postmaster scrutiny.
The InboxLee TeamApr 5DKIM 1024-bit vs 2048-bit: which one to publish in 2026
1024-bit keys still work. They are also a 1990s-era cryptographic compromise that modern enterprise mail servers are starting to flag.
The InboxLee TeamApr 4Domain age and cold email: how new is too new
Aged domains help. Brand-new domains hurt. The transition between the two is sharper than most operators expect.
The InboxLee TeamApr 2Reading Gmail Postmaster Tools as a cold-email operator
Postmaster Tools is the only direct signal Gmail gives you. Here is how to actually use it without panicking at the first red bar.
The InboxLee TeamApr 1Inbox placement vs delivery rate: stop optimising the wrong number
Delivery rate is a fictional metric. Inbox placement is the only one that matters. Here is the difference and why it costs operators their pipeline.
The InboxLee TeamMar 29MX records and cold email deliverability: the often-forgotten record
SPF, DKIM, DMARC get all the attention. MX is the one that controls what happens to bounces and replies - and it matters more than people think.
The InboxLee TeamMar 26