Deliverability
Domain & IP identity
Receiving servers trust mail that looks like who it claims to be. Here is exactly what SenderSignal validates.
Why identity matters
Spam filters ask: Does this IP belong to the hostname it claims? Does that hostname match the From domain? Is reverse DNS consistent? Misaligned identity is a common cause of deferrals even when SPF passes.
IP identity checks
Reverse DNS (PTR)
We query PTR for your sending IP. A valid PTR returns a hostname (e.g. mail.example.com).
Forward-confirmed reverse DNS (FCrDNS)
We resolve that hostname forward (A record) and confirm it maps back to the same IP. FCrDNS failure is flagged as high severity: many receivers treat it as a spam signal.
HELO/EHLO alignment
During SMTP probe we capture the server banner and compare advertised hostname to PTR. Mismatch suggests misconfiguration or shared pool without proper rDNS.
Provider detection
SenderSignal recognizes major mailbox and ESP patterns (Google Workspace, Microsoft 365, Amazon SES, SendGrid, etc.). Shared pools may have limited probe visibility: we label these provider-restricted instead of scoring them as failures.
Domain identity checks
SPF alignment path
We parse SPF includes and note whether your sending IP would pass the published SPF record for the From domain.
DKIM selector discovery
Default probes check common selectors (google, selector1, etc.). Add custom selectors in deliverability monitor rules if you use branded selectors.
DMARC alignment context
DMARC policy is evaluated alongside SPF/DKIM presence. p=none means receivers may accept failing mail: we flag it as a policy gap even when infrastructure score is high.
Domain age & DNS consistency
Where available, we note DNS consistency issues (multiple conflicting SPF records, duplicate DMARC, invalid syntax) that cause unpredictable receiver behavior.
What we display
- PTR hostname and FCrDNS pass/fail
- HELO hostname captured during SMTP
- Detected mailbox provider or ESP
- Confidence label (High / Medium / Low) when probes are partial
Fixing common issues
| Finding | Typical fix |
|---|---|
| Missing PTR | Configure rDNS with your hosting or ESP provider |
| FCrDNS fail | Ensure A record for PTR name points to sending IP |
| HELO mismatch | Set SMTP banner/HELO to match PTR hostname |
| DKIM unknown | Publish selector TXT; add selector to monitor rules |