SieveEmail validation & deliverability, explained
A plain-language guide to what Sieve checks and why it matters for anyone running email marketing. No jargon required.
What is email validation?
Email validation is the process of checking, before you hit send, whether an address is real, well-formed and safe to mail. Lists naturally decay, people change jobs, abandon inboxes, or mistype their address when they sign up. Validation catches those problems early.
Mailbox providers like Gmail and Outlook watch how your mail performs. Sending to addresses that bounce, or to spam traps, tells them you don't keep a clean list, and they respond by sending all your mail, even to your best customers, straight to the spam folder.
Cleaning a list before a campaign protects your sender reputation, lifts your open rates (because real people receive your mail), and saves money, most email platforms charge by the number of contacts you store and send to.
What the verdicts mean
Every address Sieve checks lands in one of three buckets. Each result also carries a confidence score and a per-layer breakdown so you can see exactly why it was sorted that way.
Safe to send to. The address is well-formed, the domain accepts mail, and nothing suggests it will bounce or harm your reputation.
Deliverable but with a caveat, for example a role inbox (info@, sales@), a catch-all domain, or an address we could not fully verify. Send with care, or keep it on a separate list.
Do not send. The address is invalid, a likely typo, disposable, or the mailbox does not exist. Sending to these is what drives bounces and spam complaints.
What is deliverability?
Validation is about the addresses on your list. Deliverability is about your own sending domain, whether mailbox providers trust it enough to put your mail in the inbox rather than the spam folder. A clean list sent from a poorly-configured domain still lands in spam, so the two go hand in hand.
Sieve's Deliverability check scores your domain A to F across five pillars and gives you prioritized fixes. Here's what each pillar is:
MX records tell the internet which server receives mail for a domain. No MX means the domain cannot accept email at all, an immediate red flag.
SPF is a public list of the services allowed to send mail as your domain. Without it, Gmail, Yahoo and Microsoft treat your mail as suspicious and often reject it.
DKIM adds a cryptographic signature to every message so receivers can confirm it really came from you and wasn't tampered with in transit.
DMARC ties SPF and DKIM together and tells receivers what to do with mail that fails, monitor (none), quarantine, or reject. Since 2024, bulk senders without DMARC are rejected by major providers.
Blacklists are databases of IPs and domains caught sending spam. If your sending infrastructure is listed, your mail lands in spam, or is blocked outright, until you request delisting.
Fix-it guides
Step-by-step walkthroughs for the problems the grade tool finds most often, written for people who do not live in DNS dashboards.
Your SPF record is failing and mail is landing in spam. Here is how to find the problem and publish a correct record, step by step.
Set up DKIM signing in plain steps: turn it on at your mail provider, add the DNS record at your registrar, and confirm messages pass.
Move your DMARC policy from monitoring to full enforcement without losing real mail. A phased plan with concrete steps and timelines.
Listed on a spam blacklist? Find out which list, fix the real cause, and request delisting the right way, step by step.
High bounce rate hurting your deliverability? Fix it at the source: validate addresses, prune dead ones, and keep your list clean.
A catch-all domain accepts mail to any address, real or not. Learn why that hides bad addresses and how to handle catch-alls on your list.
Glossary
A message that could not be delivered. 'Hard' bounces (the address doesn't exist) are the ones validation prevents.
A throwaway inbox from a temporary-email service. Almost never a real, lasting contact.
A shared inbox like info@, support@ or sales@. Higher complaint risk; often excluded from marketing.
A domain that accepts mail to any address, so a server can't confirm a specific mailbox exists. Marked risky, not clean.
An address used only to catch senders with poor list hygiene. Hitting one badly damages your reputation.
Mailbox providers' running score of how trustworthy your sending is. Clean lists keep it high; bounces and complaints sink it.