Guides
Guides
Five guides written in full, with the sources linked one by one. They are here because almost everything written about this is half-translated, out of date or written by whoever is selling the tool.
Start here · 11 min read
My mail goes to spam: how to find out what is really happening
There are three different things people call "going to spam", and only one of them is the spam folder. Telling them apart is 90 % of the diagnosis, and you do it by reading the bounce.
Fundamentals · 18 min read
SPF, DKIM and DMARC explained: why alignment matters
The three records, what each one is for, and the fault almost no tool names: SPF and DKIM green with DMARC failing one hundred per cent of the time.
Technical · 22 min read
Taking DMARC up to reject without breaking anything
The ladder from none to quarantine to reject after the May 2026 revision: pct is gone, sp and np do the work, and the organisational domain is resolved by walking up the tree.
Fundamentals · 13 min read
Exactly what Gmail, Outlook and Yahoo require
The three compared side by side, the 5,000 a day threshold that subdomains count towards, and the arithmetic of 0.30 %: fifteen annoyed people take you out of the system.
Technical · 14 min read
SMTP error codes: what the bounce is telling you
From 421 4.7.26 to 550 5.7.515, one by one: what it means, whether it is temporary or permanent, and what to do about each.