Koltrix
Guides
MIME 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
Blog · Guides · page 2 of 6
Guides
Step-by-step how-tos and migration checklists you can follow from start to finish.
GuidesHow to give contractors limited access to team email
A runbook for giving freelancers and agencies access to team email: own accounts, only the mailboxes they need, 2FA, an end date and a clean offboarding.
4 min read
GuidesSetting Up Email for a New Hire in Under an Hour
A new hire's email setup takes under an hour with a checklist: address, 2FA, shared mailbox access, signature, aliases and the rules of the road.
4 min read
GuidesRunning Email for Two Products From One Small Team
Two products, one small team: separate domains and reputations, shared access, distinct senders and support routing, without doubling your email work.
4 min read
GuidesSending DMARC reports to another domain: the auth record
If your rua address lives on a different domain, receivers check an authorization record first. How the _report._dmarc record works and how to test it.
4 min read
GuidesHow to plan for email volume spikes
A playbook for predictable spikes like launches and price changes and sudden ones like outages: what to prepare, how to triage the rush, and what to review.
5 min read
GuidesSending Lifecycle Emails From Your Own Job Queue
For founders who code: build onboarding and trial emails with an events table, a scheduled job and an email API, with idempotency and suppression built in.
5 min read
GuidesMTA-STS from scratch: DNS record, policy file, testing
Set up MTA-STS for inbound mail: the _mta-sts TXT record, the HTTPS policy file, testing mode, then enforce, plus the mistakes that break delivery.
5 min read
GuidesPicking a Domain With Email in Mind
Your domain ends up in every address you hand out. How to pick one that is easy to say, hard to spoof, and safe from the registrar mistakes that lose email.
4 min read
GuidesHow to write an auto-acknowledgment email that sets expectations
What an automatic reply should say, what it should never pretend, three copyable templates, and how to stop two auto-responders from emailing each other.
5 min read
GuidesTwo email providers on one domain without breaking auth
Running a workspace mailbox provider and a transactional sender on the same domain? Combine SPF, give each its own DKIM selector, and align DMARC.
5 min read
GuidesMigrating Away From Fastmail or Proton Mail: A Practical Checklist
A checklist for moving a custom domain off Fastmail or Proton Mail: exporting mail, recreating aliases, switching DNS, and the extra steps encryption adds.
5 min read