My email is not arriving
Not spam — gone. No bounce, no copy in the recipient's junk folder. That pattern narrows the cause down quickly, because a message can only disappear silently at a few points in the path.
Rejected during the SMTP transaction
If the receiver refuses with a 5xx, your own server generates a bounce — so a silent loss means the message was accepted and then discarded, or never left. The most common cause of the first is DMARC enforcement: with p=reject a receiver may reject at RCPT TO or DATA, and some large receivers accept and drop instead of bouncing, precisely to avoid backscatter.
An SPF permerror produces the same effect without any policy of your own being at fault. Over ten DNS lookups (RFC 7208 §4.6.4), or two v=spf1 records on one name, and the evaluation errors out; many receivers treat that as a fail.
Nothing to deliver to
On the receiving side the chain is MX → A/AAAA → port 25. An MX host that no longer resolves, or an MX record pointing at a CNAME (forbidden by RFC 2181 §10.3), leaves a sender with nowhere to connect. A null MX (0 ., RFC 7505) is an explicit statement that the domain accepts no mail at all.
The scan at the bottom of this page resolves every MX host and reports which ones have no address record, which are CNAMEs, and whether the domain publishes a null MX.
The delegation itself
When a registration lapses, the registry withdraws the delegation: NS, MX and A disappear from the parent zone at once. Mail then fails to resolve rather than being rejected, and the website goes down at the same moment. The scan reads the expiry date over RDAP and shows it alongside the records.
Narrowing it down
Two measurements settle most cases. The scan tells you what your DNS publishes right now. A send test pushes a real message through our MTA and reports what a receiver computes from it: the SPF result and its scope, the DKIM selector and whether the signature verified, the DMARC verdict after alignment, the PTR of your sending IP and its blocklist status.
Frequently asked questions
Why do I get no bounce?
Because the message was accepted before it was discarded. Large receivers routinely accept at SMTP time and apply policy afterwards, dropping rather than bouncing to avoid sending backscatter to a possibly forged envelope sender.
It reaches some recipients and not others.
That points at a policy difference between receivers, not at your message. Gmail and Microsoft 365 enforce DMARC alignment strictly; smaller providers often deliver an unauthenticated message that those two file or refuse.