Koltrix
Team inbox
Thread hygiene: subject lines, splits and reply-all
A checklist for keeping team email threads readable: when to split, how to rewrite subjects, trimming quotes, using reply-all well, and why threads break apart.
5 min read
DeliverabilityGmail's stricter enforcement: reading its 4xx and 5xx replies
Since late 2025 Gmail rejects more non-compliant mail outright. How to read Gmail's SMTP replies, separate temporary from permanent, and fix the cause.
5 min read
ProductHow we send ReminderIt's email
ReminderIt is our other product. Every reminder, receipt and support reply it sends goes through Koltrix. Here is the whole setup, including the awkward parts.
2 min read
DeliverabilitySPF, DKIM and DMARC in plain English
Three DNS records decide whether your email arrives. What each one actually does, what to publish, and the four mistakes that cause most of the support tickets.
4 min read
ComparisonsSelf-Hosting Email vs a Managed Provider: An Honest Cost Look
Running your own mail server buys control and costs time: reputation, patching, spam filtering, on-call. A fair look at when self-hosting makes sense.
5 min read
AI & emailWhat is MCP? A plain-English guide for email users
MCP, the Model Context Protocol, explained for people who live in email: clients and servers, how connections work, and what an email server should expose.
5 min read
StartupsCustom-domain email for indie SaaS
One to three people shipping a product need mail on their own domain, a way for the app to send, and somewhere replies land. What it costs and how to set it up.
2 min read
GuidesMoving from Google Workspace: the DNS cut-over checklist
The exact order of operations for moving a domain's email off Google Workspace without losing a single message, plus what Koltrix does not import yet.
2 min read
GuidesMIME for developers: alternative, related and mixed
Most email bugs with images and attachments are MIME tree bugs. Learn how multipart/alternative, related and mixed nest, with a correct example.
5 min read
StartupsTeam Invite Emails: Getting the Second Seat Activated
In B2B SaaS the second active user often decides whether an account sticks. How to write invite emails, reminders and expiry rules that get teammates in.
5 min read
Customer supportFully automated replies vs AI-suggested drafts in support
Where fully automated support replies are fine, where AI-suggested drafts reviewed by an agent fit better, and a decision table for your own message types.
5 min read
DeliverabilityDANE vs MTA-STS for inbound mail: the trade-offs
Both stop STARTTLS downgrades, with different trust models. Compare DANE's DNSSEC dependency with MTA-STS's web PKI approach and decide what to deploy.
5 min read