Tools
Every check a receiving mail server runs
Eleven lookups, grouped by the gate they belong to. Each page explains what the check reads, what a passing answer looks like, and what to change when it fails.
Routing
Which hosts are told to accept mail for the domain, and whether they answer.
- MX lookup MX records are the first thing a sending server asks DNS for. SenderProbe reads every mail exchanger a domain publishes, resolves the hosts behind them, opens a connection to each one and reports which part of the routing is missing.
- A record lookup Every connection to a domain begins by resolving it to an address. SenderProbe queries every resolver it is configured with, compares the answers so a half-finished change is visible, and reads the reverse DNS of each address it finds.
- NS record lookup Every other record depends on this one. SenderProbe reads the NS records a domain is delegated to, resolves each nameserver to make a lame delegation visible, and compares what the resolvers it queries have to say about the delegation.
Authentication
Whether the receiver can prove the message came from you, and what your policy asks it to do when it cannot.
- SPF record checker SPF states which hosts may use your domain in the envelope sender. SenderProbe fetches the record, walks every include, counts the DNS lookups an evaluation would make and names the terms that would make a receiver stop reading.
- DKIM record checker A DKIM signature is only as good as the key a receiver can fetch to verify it. SenderProbe probes the common selector names, reads the key material each one publishes, and reports its type, its length and the flags that quietly disable it.
- DMARC record checker DMARC is where SPF and DKIM stop being diagnostics and start being a decision. SenderProbe reads the record, falls back to the organisational domain the way a receiver does, and reports the policy that will actually be applied.
Reputation
What the sending address looks like to a filter before it reads a single word.
- Blacklist check Reputation is judged before a filter reads a word of your message. SenderProbe resolves the addresses behind a domain, queries every blacklist zone it knows in parallel, and returns the listing reason and the delisting route for each one that answers.
- Reverse DNS lookup A receiving server asks who an address says it is before it accepts anything from it. SenderProbe resolves the addresses behind a domain, reads the PTR record for each, and confirms that the name it returns resolves back to the same address.
Transport and ownership
The live SMTP conversation, the certificate it offers, and the records and registration behind the domain.
- SMTP server test The records can all be correct and the conversation still go wrong. SenderProbe resolves the MX records for a domain, holds a real SMTP session with the primary mail host, and returns the transcript alongside what it learned from each line.
- TXT record lookup The apex of a busy domain collects TXT records the way a drawer collects cables. SenderProbe reads all of them, labels the ones it recognises, and says plainly whether the SPF policy among them is valid or duplicated.
- WHOIS lookup Every record you publish rests on a registration that somebody has to renew. SenderProbe queries the registry and the registrar, parses the fields each spells differently, and reports the expiry date, the status codes and the locks the domain carries.
Run all eleven against your domain. One sweep reads the records, the reputation and the SMTP conversation, and scores the result.
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