Email Deliverability Test
Send one real email to check SPF, DKIM, DMARC, sending-IP reputation, and content signals — with fixes ranked by impact.
One email. Three layers checked.
We create a private test address. Send it the same email your customers receive, and your report appears here automatically.
Authentication
SPF, DKIM, DMARC & alignment
Reputation
Sending IP & major blocklists
Content
Filter signals & prioritized fixes
Free · No signup · Results in about 30 seconds
Find the cause, not just the symptom
Inbox placement snapshots tell you where one message landed. This test tells you why it may be filtered. It captures a real email from your real sending infrastructure, checks SPF, DKIM, and DMARC alignment, inspects the sending IP across major blocklists, and reviews message-level filter signals. Every issue comes with a concrete next step, starting with the authentication layer you fully control.
Email deliverability knowledge base
The terms behind email deliverability: authentication headers, delivery paths, and blocklists.
Email headers
- Received
- The delivery trail. Every mail server that handles the message prepends its own Received line, so reading them bottom-up traces the path from the origin server to your inbox — including hostnames, IPs, and timestamps for each hop.
- Authentication-Results
- Added by the receiving mail server to record its SPF, DKIM, and DMARC verdicts (RFC 8601). This is the header an analyzer reads to tell you whether the message passed authentication and for which domains.
- From
- The visible sender shown in your mail client. It’s trivial to forge, which is exactly why DMARC exists: DMARC checks that the domains SPF and DKIM validated align with this From domain.
- Return-Path
- The envelope sender (RFC5321.MailFrom) where bounces are sent, stamped by the receiving server. SPF is evaluated against this domain — if it doesn’t align with the From domain, an SPF pass won’t help the message pass DMARC.
- Reply-To
- Where replies go when it differs from the From address. Legitimate for shared inboxes and newsletters, but a Reply-To pointing at an unrelated domain is a classic phishing tell.
- Message-ID
- A globally unique identifier assigned when the message is created, usually ending in the sending domain. Missing, duplicate, or mismatched Message-IDs are a spam and spoofing signal.
- DKIM-Signature
- The cryptographic signature the sending domain attaches to the message. It names the signing domain (d=) and selector (s=) used to fetch the public key from DNS, letting receivers verify the message wasn’t altered in transit.
- Received-SPF
- An older per-hop record of the SPF check result, including the client IP that was evaluated. Useful as a fallback when there’s no Authentication-Results header.
- ARC-Seal
- Part of ARC (Authenticated Received Chain). Forwarders and mailing lists use ARC headers to preserve the original authentication results, so a receiver can still trust a message whose SPF/DKIM broke in forwarding.
- X-Mailer
- The software that composed the message (e.g. Outlook, a CRM, a bulk sender). Optional and easily faked, but handy for spotting mail that claims to be personal yet was sent by automation.
- List-Unsubscribe
- The machine-readable unsubscribe method (mailto: and/or URL) that powers the one-click unsubscribe button. Gmail and Yahoo require it for bulk senders.
Blocklists
- DNSBLDNS blocklist
- A blocklist published over DNS. A receiving mail server checks a sending IP by querying the reversed IP under the list's zone; an answer means the IP is listed. Also called an RBL (Realtime Blackhole List) or blacklist.
- SBLSpamhaus Block List
- Spamhaus's list of IPs from which they do not recommend accepting email, based on evidence of spam operations. Part of the combined ZEN zone.
- XBLExploits Block List
- Spamhaus's list of hijacked machines, proxies, and malware-infected hosts. Being on the XBL usually means a device on your network is compromised, not that you sent spam deliberately.
- PBLPolicy Block List
- Spamhaus's list of IP ranges that should not be sending mail directly to the internet (e.g. residential/dynamic IPs). Sending from a PBL-listed IP means you should relay through your provider's mail server instead.
- listing
- The state of an IP or domain appearing on a blocklist. A listing returned by a lookup is typically an address in the 127.0.0.0/8 range, where the last octet encodes why it was listed.
- delisting
- Removing an IP or domain from a blocklist. Most operators offer a self-service removal form, but delisting only sticks if the underlying problem (spam, a compromised host, poor authentication) is fixed first.
- spamtrap
- An email address that never opts in and exists only to catch spam. Mail sent to a spamtrap is strong evidence of a bad list or scraped addresses and is a common cause of a listing.
- snowshoe
- Spreading spam thinly across many IPs and domains to stay under per-source volume limits. Blocklists specifically hunt for snowshoe patterns.
- PTRReverse DNS
- The PTR record maps a sending IP back to a hostname. A missing or generic PTR record makes an IP look untrustworthy and contributes to listings and filtering.
- 127.0.0.xReturn code
- The A-record value a DNSBL returns for a listed IP. Different last octets mean different sub-lists or reasons. A 127.255.255.x value is not a real listing — it signals the query was refused (often because it came from a large shared resolver).