Infrastructure Engineer. I work on the systems that carry high-volume email: MTA platforms, SMTP transport, sender reputation, and the authentication stack of SPF, DKIM and DMARC.
Most of what I publish here comes out of running that infrastructure rather than reading about it. The tools started as scripts for problems I hit at three in the morning, and the reference pages exist because the answer I needed was spread across an RFC, a vendor page and a mailing list post from 2009.
rastu.tech is a set of browser tools for email infrastructure and deliverability. Nothing is uploaded and there is no account: the lookups run from your own machine.
| Tool | What it does |
|---|---|
| Warm-up planner | A ramp to a target volume, split by mailbox provider, gated on the metric that has to hold before each step rather than on the calendar |
| Blocklist check | Confirms each list is still answering correctly before reporting its result. A zone that has been shut down answers nothing, which is the same answer it gives for an address that is not listed |
| DMARC report reader | Computes alignment from the authentication results rather than trusting the reporter's own verdict, and shows what moving to p=reject would actually do |
| Header analyser | Says whether a problem is yours, the receiver's, or an intermediary's, and reads the signature tags a DNS-based checker structurally cannot see |
| Domain check | SPF, DKIM, DMARC, MTA-STS, TLS-RPT and BIMI, including whether a policy really exists behind the record that promises one |
| SPF lookup counter | The RFC 7208 ten-lookup ceiling, counted properly, including the void lookups that also count |
| Bounce classifier | An SMTP response turned into a category and an action. Hard and soft is too coarse to act on |
Alongside them: every current email RFC with the sentences that bind an implementation pulled out, and a searchable reference of SMTP responses drawn from RFC 5321, the IANA registry and the providers' own documentation.
- rastu.tech: the site and the tools
- smtpsift: classify SMTP rejections and deferrals into a category and an action
- dmarcsight: audit a domain's authentication posture end to end
- email-rfcs: every current email RFC indexed, with obsoletion chains resolved
- smtp-responses: SMTP responses parsed from the standards and the registries
Every tool refuses to give a confident wrong answer. If something cannot be determined it says so and says why, because in this field a false clean result costs more than no result: somebody acts on it.
That principle is enforced rather than intended. The build fails on a schedule that drifts from the document it cites, on a claim carrying a number its source does not publish, and on a result that explains its own method instead of stating a finding.
The state of email authentication, measured across
100,000 domains from the Tranco list. 58.7% publish DMARC and 20.9% reach
p=reject; of those publishing at all, 35.8% sit at p=none where it blocks
nothing. Methodology and the raw dataset are published alongside it.
doi:10.5281/zenodo.22832936 · CC BY 4.0
rastu.tech · LinkedIn · ORCID