Koltrix
Deliverability
Why two SPF records are worse than none
Publishing a second SPF TXT record makes every check a permerror. How it happens, how to detect it with dig, and how to merge records safely.
4 min read
- Guides
Email not received? A systematic debugging order
When a customer says your email never arrived, work the problem in order: your logs, the SMTP response, authentication, filtering, then the recipient.
4 min read
- Deliverability
DKIM body hash did not verify: the usual suspects
When DKIM fails with a body hash mismatch, something changed the message after signing. Find the culprit: footers, rewriters, line endings, encoding.
4 min read
Guidesdig commands every email engineer should know
The dig queries that answer most email questions: SPF, DKIM selectors, DMARC, MX, PTR, MTA-STS and BIMI, plus how to bypass caches when testing.
5 min read
GuidesTracing a delivery through Received headers
Received headers record every hop a message took, newest first. Read them bottom-up to find delays, rewrites and the server that touched your mail.
5 min read
GuidesReading Authentication-Results headers like a receiver
The Authentication-Results header records the SPF, DKIM and DMARC verdicts a receiver reached. Decode each field and use it to debug failures fast.
5 min read