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Email Deliverability, Explained

Plain-language answers to the questions people actually search for — no marketing fluff, just how email deliverability actually works, sourced to RFCs and major provider documentation.

Verification Basics

How Does SMTP Email Verification Work?

SMTP verification checks whether a specific mailbox exists by connecting directly to the recipient's mail server and initiating (b...

What Is a Catch-All Email Domain?

A catch-all (or "accept-all") email domain is configured to accept mail sent to any address at that domain, even ones that don't c...

What Is a Null MX Record?

A null MX record is a special DNS entry (defined by RFC 7505) that explicitly declares a domain does not accept email at all, usin...

What Is a Role-Based Email Address?

A role-based email address is a mailbox tied to a function or department rather than an individual person — like info@, support@, ...

What Is an MX Record?

An MX (Mail Exchange) record is a DNS entry that specifies which mail server(s) are responsible for receiving email on behalf of a...

What Is Plus Addressing (Subaddressing) in Email?

Plus addressing (also called subaddressing or tagged addressing) lets a user append a "+tag" to the local part of their email addr...

What's the Difference Between Email Validation and Verification?

Email validation checks that an address is correctly formatted and the domain has valid DNS/MX records — a syntax and structure ch...

What Is DKIM (DomainKeys Identified Mail)?

DKIM (DomainKeys Identified Mail) adds a cryptographic signature to outgoing email, generated with a private key, that receiving s...

What Is DMARC (Domain-based Message Authentication)?

DMARC (Domain-based Message Authentication, Reporting & Conformance) is a DNS policy record that tells receiving mail servers what...

What Is SPF (Sender Policy Framework)?

SPF (Sender Policy Framework) is a DNS TXT record that lists which mail servers are authorized to send email on behalf of a domain...

What Is a Feedback Loop (FBL) in Email?

A feedback loop (FBL) is a service some mailbox providers offer that automatically notifies a sender whenever a recipient marks th...

What Is a Safe Email Bounce Rate in 2026?

A safe hard-bounce rate is generally considered to be under 2%, with under 1% recommended for senders using Gmail's or Yahoo's bul...

What Is an Email Blocklist (Blacklist)?

An email blocklist (sometimes called a blacklist) is a database of IP addresses or domains identified as sources of spam, malware,...

What Is Greylisting in Email Delivery?

Greylisting is a spam-prevention technique where a receiving mail server temporarily rejects an email from an unrecognized sender ...

What Is Inbox Placement Testing?

Inbox placement is where a delivered email actually ends up — primary inbox, a tabbed category like Promotions, or the spam folder...

What Is Sender Reputation in Email?

Sender reputation is a score mailbox providers assign to a sending domain and IP address based on historical behavior — bounce rat...

What's the Difference Between Email Delivery and Deliverability?

Email delivery means a message was accepted by the recipient's mail server without being rejected or bounced. Email deliverability...

What Is a Disposable Email Address?

A disposable email address is a temporary inbox from a service like Mailinator, Yopmail, or Guerrilla Mail, designed to receive a ...

What Is a Hard Bounce in Email Marketing?

A hard bounce is a permanent delivery failure — the receiving mail server rejects the message outright, typically because the mail...

What Is a Honeypot Email Address?

A honeypot email address is an address deliberately planted in a location where only automated scrapers would find it (like hidden...

What Is a Soft Bounce in Email Marketing?

A soft bounce is a temporary delivery failure — the mailbox exists but the message couldn't be delivered right now, commonly becau...

What Is a Spam Trap Email Address?

A spam trap is an email address specifically created (or abandoned and repurposed) by mailbox providers, anti-spam organizations, ...

What Is Double Opt-In for Email Lists?

Double opt-in is a signup process where a new subscriber must confirm their email address by clicking a verification link sent aft...

What Is Email List Decay?

Email list decay is the natural, ongoing process by which a percentage of an email list becomes invalid over time — as people chan...

What Is BIMI (Brand Indicators for Message Identification)?

BIMI (Brand Indicators for Message Identification) is an email standard that lets a verified brand logo appear next to authenticat...

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