Koltrix
Deliverability
Domain reputation vs IP reputation: which is hurting you?
Modern filters weigh your domain more heavily than your IP, but both matter. How to tell which one is dragging placement down and what fixes each.
4 min read
Email APIPer-provider throttling: pacing mail to big mailbox providers
Gmail, Outlook and Yahoo each defer differently when you send too fast. Build per-destination queues and adaptive concurrency that respond to 4xx replies.
4 min read
DeliverabilityReverse DNS for mail servers: PTR, FCrDNS and HELO
Receivers expect a sending IP to have a PTR record that resolves back to the same IP and a sane HELO name. Configure all three and verify them.
4 min read
DeliverabilityShared vs dedicated sending IPs: a decision guide
Dedicated IPs give you control and responsibility; shared pools give you a neighbor's reputation. Volume thresholds and questions to decide well.
4 min read