Koltrix
Comparisons
Fastmail vs Proton Mail for Small Business Email
Fastmail and Proton Mail are the two independent mailbox hosts small teams ask about most. How they differ on privacy, desktop clients and daily team use.
5 min read
AI & emailMeasuring AI triage accuracy in your own inbox
A worked example of testing AI email sorting on your own mail: sample 200 messages, label them by hand, build a confusion matrix and weigh costly errors.
5 min read
DeliverabilityIP warm-up: a realistic schedule and what to watch daily
A practical IP warm-up plan that ramps volume over weeks, prioritizes engaged recipients and backs off on deferrals, with daily signals to check.
4 min read
StartupsThe Cancellation Confirmation Email Most SaaS Teams Get Wrong
The email you send when a customer cancels shapes whether they ever come back. What a respectful cancellation confirmation says, and the patterns to avoid.
4 min read
Team inboxDesigning per-mailbox permissions for a growing team
Map roles to shared mailboxes with a permission matrix, apply least access, keep billing and legal mail narrow, and set a review cadence as your team grows.
4 min read
Email APIMessage-ID, In-Reply-To and References for app email
Control how notification emails thread in Gmail and Outlook with Message-ID, In-Reply-To and References, and how to break unwanted threads apart.
4 min read
GuidesBefore Any Email Migration: Inventory Everything That Sends as You
Most email migrations break something nobody listed: a CRM, a form, a scanner. How to find every service that sends as your domain before you change DNS.
4 min read
Customer supportEscalation paths for email support that actually work
How a small company can design email support escalation: tiers, clear criteria, telling the customer, keeping frontline ownership, and avoiding ping-pong.
4 min read
DeliverabilityGreylisting and 4xx deferrals: why your retries matter
Greylisting temporarily rejects unknown senders and expects a retry. How it works, what deferrals look like in logs and the retry behavior receivers expect.
4 min read
StartupsInvoluntary Churn: Fixing Expiring Cards Before They Fail
Customers who leave because a card expired never meant to leave. How to track expiry dates, send pre-expiry emails that work, and measure the revenue you keep.
4 min read
AI & emailAI thread summaries: when they help and when to read the original
AI thread summaries are great for catching up and risky for contracts, numbers and tense conversations. A decision table and a spot-check habit for using them.
4 min read
GuidesTesting SMTP by hand with swaks and openssl
Talk to a mail server directly to see what it really says. Use swaks and openssl s_client to test auth, TLS, relaying and rejections step by step.
5 min read