Koltrix
Deliverability
Gmail and Yahoo bulk sender rules: the full checklist
What Gmail and Yahoo require from senders of roughly 5,000 messages a day: SPF and DKIM, DMARC, alignment, one-click unsubscribe and spam rates.
4 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
DeliverabilityGoogle Postmaster Tools: the dashboards that matter
Postmaster Tools is the only first-party view into how Gmail sees your domain. Set it up, read the spam rate and compliance views, and know its blind spots.
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
DeliverabilityWhy transactional email lands in Gmail Promotions
Receipts and alerts in the Promotions tab are usually a content and stream problem. The signals Gmail likely uses and changes that tend to help.
4 min read
DeliverabilityTransactional vs marketing mail under bulk sender rules
Which bulk sender rules apply to receipts and password resets, which apply only to marketing, and why mixing both streams on one domain is risky.
4 min read