Koltrix
Deliverability
The case against noreply@ addresses
A noreply sender discards replies that signal engagement and frustrates customers. Route replies to a real inbox instead and set expectations clearly.
4 min read
DeliverabilitySeparate subdomains for transactional and marketing mail
Splitting streams across subdomains contains reputation damage. How to structure them, align SPF and DKIM per subdomain, and what it cannot protect.
4 min read
DeliverabilityCustom tracking domains and why shared link domains hurt
Click tracking rewrites links through a redirect domain. If that domain is shared, its reputation becomes yours. Set up a branded one with HTTPS.
4 min read
DeliverabilityDomain 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
DeliverabilityThe 0.3% spam rate line: how it is measured and avoided
Gmail and Yahoo both draw a line at a 0.3% spam complaint rate and recommend staying under 0.1%. How the rate is calculated and how to keep it low.
4 min read
DeliverabilityDetecting a compromised account sending spam as you
A hijacked mailbox or leaked SMTP credential can burn your domain reputation in hours. The signals to watch and the containment steps to rehearse.
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
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
DeliverabilitySpamhaus listings explained: SBL, XBL, PBL, CSS, DBL
Spamhaus runs several blocklists with different causes and fixes. What each one means for a sender, how to check a listing and where to start.
5 min read
- Deliverability
DKIM replay attacks: how signed mail gets abused
A single legitimately signed message can be resent to millions. How DKIM replay works, why it hurts your domain, and the mitigations available today.
4 min read
DeliverabilitySpam traps: pristine, recycled and typo traps explained
Spam traps are addresses that should never receive your mail. How each type ends up on lists, what hitting them signals and how to stop it happening.
5 min read