Deliverability
Deliverability guides and product notes — no filler.
Spam complaint rate: the number that decides deliverability
Your spam complaint rate is complaints divided by delivered mail. Learn the 0.3% limit, the 0.1% target, and how to measure and reduce complaints.
Spam trigger words: the myth vs what filters weigh
Spam trigger words are mostly a myth: modern filters weigh reputation, authentication and list quality far more than any word in your copy.
The Barracuda blacklist (BRBL), explained and delisted
The Barracuda blacklist (BRBL) lists IPs with poor sending reputation. How to check, request free removal, and stay off it for good.
Proofpoint Dynamic Reputation and why enterprise mail gets blocked
Proofpoint Dynamic Reputation (PDR) blocks mail only to enterprise inboxes. How the Proofpoint blacklist works, and how to check and fix it.
Cold email deliverability: how to reach the inbox
Cold email deliverability is hard: no engagement and dirty lists. The levers that get cold outreach to the inbox — starting with verification.
SpamCop blacklist: how it lists and self-clears
The SpamCop blacklist (SCBL) lists sending IPs from spam reports and traps, then expires on its own. How it works, how to check, and how to get off.
The UCEPROTECT blacklist and its three levels, explained
How the UCEPROTECT blacklist's three levels work, why you can be listed through no fault of your own, the free-wait vs paid-express debate, and more.
SpamRats blacklist: why reverse DNS gets you listed
Why the SpamRats blacklist lists IPs for missing reverse DNS, how to check your PTR record, and how to fix and delist for free.
Invaluement blacklist: why your clean IP still gets blocked
Invaluement is a low-false-positive DNSBL that lists spam domains found in message bodies — so a link in your content can block mail from a clean IP.
The CBL blacklist and why a listing means you're compromised
The CBL flags IPs sending botnet and malware traffic. Learn why clean business IPs get listed, how it feeds Spamhaus XBL, and how to self-delist.
Email feedback loops (FBLs) explained
Email feedback loops forward spam complaints back so you can suppress complainers. How they work, which providers offer them, and why Gmail is different.
Dedicated vs shared IP for email sending
Dedicated vs shared IP for email: how each affects reputation and warmup, the volume that justifies a dedicated IP, and which one you should choose.