Glossary
Technical terms used in email verification, deliverability, and security. Click any term to learn more.
Email Verification
The process of validating whether an email address is deliverable and belongs to a real inbox. Includes syntax check, domain validation, MX lookup, SMTP handshake, and disposable email detection.
Bounce
An email that is returned to the sender because it could not be delivered. Hard bounces are permanent (invalid address), soft bounces are temporary (mailbox full, server timeout).
Hard Bounce
A permanent delivery failure. The email address does not exist, the domain is invalid, or the mail server refuses the message permanently. Hard bounces should be removed from your list immediately to protect sender reputation.
Soft Bounce
A temporary delivery failure. The email address exists but the message could not be delivered due to a full mailbox, server timeout, or rate limiting. Soft bounces may succeed on retry, but repeated soft bounces should be monitored.
Catch-All
A mail server configuration that accepts all emails sent to a domain, regardless of whether the specific address exists. This makes standard SMTP verification unreliable and requires deep catch-all detection techniques that probe the server's behavior.
SPF (Sender Policy Framework)
An email authentication protocol that specifies which mail servers are authorized to send emails for a domain. Published as a TXT record in DNS. Helps prevent sender forgery and reduces spam.
DKIM (DomainKeys Identified Mail)
An email authentication method that uses a digital signature to verify that an email was not tampered with during transit. The signature is verified against a public key published in the sender's DNS records.
DMARC (Domain-based Message Authentication, Reporting & Conformance)
A policy framework that builds on SPF and DKIM. It tells receiving mail servers what to do if an email fails authentication — quarantine, reject, or take no action — and provides detailed reports on authentication results.
BIMI (Brand Indicators for Message Identification)
A specification that enables brands to display their logo next to authenticated emails in supporting email clients. Requires DMARC enforcement (p=quarantine or p=reject) and a Verified Mark Certificate (VMC).
Spam Trap
An email address specifically created to catch spammers. Pristine traps have never been used for signups and can only receive mail from list scraping or dictionary attacks. Hitting a spam trap severely damages sender reputation.
MX Record (Mail Exchange)
A DNS record that specifies the mail server responsible for receiving emails on behalf of a domain. MX records are checked during email verification to confirm the domain can receive mail and to identify the mail server.
SMTP (Simple Mail Transfer Protocol)
The standard protocol used for sending emails across the internet. Email verification tools use SMTP handshakes to check if a mailbox exists without actually sending a message. Bextrad uses SMTP for real-time verification.
Disposable Email
A temporary email address from services like Mailinator, Guerrilla Mail, or Temp Mail. These addresses expire quickly and are often used to bypass signup forms. Bextrad detects and flags them automatically during verification.
Blacklist / DNSBL
A DNS-based blocklist that tracks IP addresses and domains known for sending spam. If your sending IP is listed, email providers may reject or quarantine your messages. Bextrad checks against multiple blacklists in real time.
MTA-STS (Mail Transfer Agent Strict Transport Security)
A security protocol that enforces TLS encryption for email delivery between mail servers. Published as a DNS TXT record and a policy file on a web server. Prevents downgrade attacks on SMTP connections.
Syntax Validation
The first step of email verification that checks whether an email address conforms to RFC 5321/5322 standards. Validates format, length, character placement, and ensures exactly one @ symbol.
Role-Based Email
An email address tied to a function rather than a person (e.g., info@company.com, support@company.com, admin@company.com). Role-based addresses often bounce and have lower engagement rates, so many senders exclude them.
Suppression List
A list of email addresses that should never be sent to again — hard bounces, spam complaints, and unsubscribes. Maintaining a suppression list is essential for sender reputation and legal compliance (CAN-SPAM, GDPR).
Email Deliverability
The ability of an email to reach the recipient's inbox rather than being filtered to spam or rejected. Factors include sender reputation, authentication (SPF/DKIM/DMARC), bounce rate, content quality, and list hygiene.
Rate Limiting
The practice of controlling the number of emails sent or verified within a specific time window. Prevents server overload, avoids SMTP throttling by receiving servers, and protects sender reputation from aggressive sending patterns.