Reference
glossary
Plain-language definitions for every email verification, deliverability, and compliance term you'll encounter — with practical examples for each.
B
Bounce rate
The percentage of emails sent that could not be delivered. Split into hard bounces (permanent failures — address doesn't exist) and soft bounces (temporary failures — inbox full, server down).
Example: Send 1,000 emails and 30 bounce — bounce rate is 3%. Most ESPs warn at 2% and suspend accounts above 5%.
C
Catch-all email (accept-all)
A domain configured to accept mail for any address, regardless of whether the specific mailbox exists. The mail server returns a positive SMTP response but may silently discard the message.
Example: [email protected] is accepted even if that mailbox doesn't exist. VerifiSaaS flags catch-all domains with a lower confidence score.
D
DKIM (DomainKeys Identified Mail)
A cryptographic email authentication method that adds a digital signature to outgoing emails. Receiving servers verify this signature to confirm the email wasn't modified in transit.
Example: Without DKIM, a receiving server can't tell if your email was modified after leaving your server. Gmail shows warnings for unsigned emails from bulk senders.
DMARC
Domain-based Message Authentication, Reporting, and Conformance. A DNS policy telling receiving servers what to do when an email fails SPF or DKIM checks — quarantine, reject, or monitor.
Example: v=DMARC1; p=reject; tells servers to reject emails failing authentication. Required by Google & Yahoo since 2024 for bulk senders.
Disposable email address (DEA)
A temporary email address created to bypass signups. Created through Mailinator, Guerrilla Mail, 10 Minute Mail, and thousands of similar services. Disposable addresses inflate your list but never convert.
Example: [email protected] — VerifiSaaS maintains a database of 20,000+ disposable domains and flags them automatically.
E
Email validation
Checking that an email address is correctly formatted per RFC 5322 standards. Validation checks syntax; verification goes further to check DNS records, mailbox existence, and risk signals.
Example: user@example fails validation (missing TLD). [email protected] passes validation but could still be an invalid mailbox — only verification confirms it.
H
Hard bounce
A permanent email delivery failure. The address doesn't exist, the domain has no mail server, or the server permanently rejected delivery. Hard bounces signal list hygiene problems to ESPs.
Example: Sending to [email protected] — the MX record no longer exists. Delivery fails permanently. VerifiSaaS catches these before you send.
M
MX record (Mail Exchange record)
A DNS record that specifies which mail server handles email for a domain. If a domain has no MX record, no email can be delivered to it. VerifiSaaS checks MX records as a core step in the verification process.
S
Sender reputation
A score assigned by ISPs based on your sending history — bounce rates, spam complaints, open rates, and volume. Low sender reputation means your emails land in spam or get blocked entirely.
Example: If your bounce rate exceeds 5% over 30 days, Gmail Postmaster Tools will show your domain reputation dropping from "High" to "Low".
Sender score
A 0–100 numerical measure of your sending reputation. Above 80: good standing. Below 70: deliverability problems. Below 50: ISPs may block your email entirely.
Soft bounce
A temporary email delivery failure. Causes: full inbox, server temporarily down, message too large. Unlike hard bounces, soft bounces may self-resolve on retry. ESPs retry 3–5 times over 72 hours.
Spam trap
An email address used by ISPs to identify senders with poor list hygiene. Types: recycled (old addresses repurposed) and pristine (addresses never owned by humans, only scraped). Sending to a trap triggers blocklisting.
Example: An ISP creates [email protected] — never published anywhere. If you're sending to it, you scraped or bought a list. VerifiSaaS checks against known trap networks.
SPF (Sender Policy Framework)
A DNS record listing which IP addresses are authorised to send email for your domain. Receiving servers check SPF to detect spoofed "From" addresses.
Example: v=spf1 include:sendgrid.net ~all — authorises SendGrid to send on your behalf. Without SPF, emails are more likely to be marked spam.
U
Unsubscribe rate
The percentage of recipients who click "unsubscribe" after receiving a message. Above 0.5% signals poor targeting or list quality. Like bounce rate, it affects your sender reputation with ISPs.
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