Everything on the blog filed under deliverability, newest first.
Which sending setup survives cold outreach and which one gets you suspended — mailboxes versus bulk senders, domains versus subdomains, aliases versus real inboxes, and the limits that actually bind.
What SMTP reply codes mean, which bounces damage your domain and which are harmless, and the exact rules for when to retry, when to suppress and when to stop the campaign.
What happens when an address is checked — syntax, MX records and the SMTP probe — and why "risky" is a real answer rather than a hedge. Written from the inside of a verifier.