Resources for a presentation Steve gave at the Deliverability Summit 2026 in Barcelona.
Deck
The deck, DeliverySummit2026.pdf.
EmailGeeks Slack
Join the Slack at email.geeks.chat.
Don’t let them type it in
Comparing DKIM Keys is where I wrote this up at the time, and shows the various ways I compared the keys.
Not that algorithm
Redsift’s blog post about Ed25519 support.
Tools
Some of the tools I used to do the research behind this, or to diagnose real problems.
About My Email
AboutMy.Email is a tool I wrote to automate many of the checks I do looking for emailstructure and authentication issues.
Web based tools
tools.wordtothewise.com is our suite of web based tools for checking DNS and authentication.)
dnstrace
There are several tools called dnstrace which do roughly the same thing - resolve DNS for a hostname, checking responses from all the nameservers that may affect the result, finding misbehaving servers in the resolution path.
The original, from the djbdns package, includes dnstrace and dnstracesort. It’s available from most Linux package managers and is the one I tend to use most of the time. It’s a little quirky, though, and displays some of it’s results in tinydns format rather than standard DNS format so it’s not the easiest to approach.
rs/dnstrace is a much more modern version. It performs a lot of queries in parallel and runs much faster. Nice colour output too.
dig
dig is the standard tool for doing DNS queries. It’s quite verbose, giving a lot more details about the response than some other tools (including most web based ones).
If you’re checking for response size, additional response records, CNAMEs, whether a server is authoritative or not then those extra details are useful.
There are some installation instructions and alternatives here.
spf
wttw/spf is a commandline tool that evaluates an SPF record for an email, showing every step of the SPF evaluation so you can see where a term that you expected to lead to a pass result doesn’t. (It’s the same engine aboutmy.email uses on it’s SPF tag, so if you can use that you don’t need the CLI tool).
dkimsign, dkim-keygen, dkim-verify
dkimsign contains a few tools for commandline DKIM signing and verification.
swaks
swaks makes injecting a message in a file into a mailserver easy. If you’re using it on macOS then this might be useful.
dnssec
The Verisign dnssec debugger is the tool I use for checking DNSSEC. Not having DNSSEC is OK, but having missing DNSSEC on a subdomain where the parent domain expects it can be a problem.