Syntax vs. SMTP Verification: What Each Layer Actually Catches

Spamify’s email checking is built from two independent layers. They catch different classes of bad address, and understanding the split is the key to tuning the plugin well.

Layer 1 — Syntax validation (always on)

The syntax layer runs entirely on your server, on every submission, with no outbound connection. It confirms the address is well-formed and rejects the obviously broken and obviously fake:

• Malformed structure — missing @, double dots, illegal characters.
• Keyboard-mash and gibberish local parts.
• Domains that can’t resolve to a mail host at all.

Syntax validation is fast, private, and free — it’s the floor under everything else, and it can never be turned off.

Layer 2 — SMTP mailbox verification (optional, off by default)

Syntax can tell you john@gmial.com is structurally valid — but not that the mailbox doesn’t exist. That’s what the SMTP layer does. When enabled, Spamify opens a direct connection to the recipient domain’s own mail server (its MX host) and performs an SMTP handshake asking whether the mailbox exists. No email is ever sent, and nothing goes to the plugin author or any third party.

This catches the addresses that pass syntax but are still dead: typo’d real domains, abandoned mailboxes, and made-up local parts on real domains.

Which should you rely on?

The catch with SMTP

Many hosts block outbound port 25, and many mail servers greylist or use catch-all addresses — so a mailbox can’t always be confirmed. Spamify treats those as unverifiable rather than bad, and by default flags them for review instead of blocking. See why submissions come back unverifiable and how to enable SMTP verification safely for the details.