What this analysis does
Compare the current public state with a proposed configuration and see lookup pressure, policy changes and likely authentication consequences before making the change.
Email DNS changes are published to a global cache that cannot be recalled on demand. A proposed record can be resolved and measured before it reaches production, which converts an irreversible change into a reviewable one.
Compare the proposal against the live baseline
The simulator first resolves the domain’s currently published policy, then resolves the proposed record with the same recursive method. Reporting both sides is what makes the result actionable: an absolute lookup count means little without knowing whether the change increases or decreases pressure relative to what is live today.
The delta is the number to review in a change ticket. A proposal that reduces dependency pressure is safe to schedule normally. A proposal that increases it deserves scrutiny even when it stays under the limit, because the next vendor addition will start from that higher baseline.
- Both the live and proposed records are resolved recursively.
- The reported delta is the change in DNS-triggering mechanisms.
- Staying under the limit is necessary but not sufficient; headroom matters.
Lower the TTL before the change, not during it
A record cached at a long TTL keeps serving the old value after you publish a new one. Reducing the TTL well ahead of a change shortens that window, but only if it is done far enough in advance for the old TTL itself to expire everywhere. Lowering it at the moment of the change provides no benefit.
Plan the sequence explicitly: reduce TTL, wait for the previous TTL to elapse, publish the change, verify from multiple vantage points, then restore the normal TTL. Skipping the wait is the most common reason a change appears to work for some senders and not others.
Verify with a real message afterwards
A record that resolves correctly has not yet been proven in production. The authoritative confirmation is a real message: send to a test recipient after propagation and read the Authentication-Results header the receiver stamped, along with the Return-Path that SPF actually evaluated.
That step catches the class of problem simulation cannot see, where the record is valid but the sending platform uses a different envelope domain than expected. Configuration screens describe intent; headers describe what the receiver observed.
Read the resulting message headersDiff the before and after DNS state
Example: adding a vendor to a record near the limit
Evidence supplied
Current policy resolves to eight DNS-triggering mechanisms. The proposal adds one further include.
How to read the result
The simulation reports the new total, the delta of the change and whether the proposal crosses the evaluation limit. A result that lands at ten is flagged as having no remaining headroom, even though it does not yet produce PermError.
Known limits
- Simulation resolves vendor policies as they exist now; a provider can expand its own record later.
- Propagation behaviour depends on resolver caching that no single vantage point can fully observe.
- A valid record does not guarantee that the sending platform will use the expected envelope domain.
Common questions
Can I test a DMARC change the same way?
Policy discovery and alignment are modelled separately. Use the DMARC alignment lab and tree walk explorer for policy changes, and this simulator for SPF dependency pressure.
How long should I wait after publishing?
At least the previous TTL of the record being replaced, and longer where intermediate resolvers are known to extend caching.
Does a passing simulation mean mail will authenticate?
No. It means the proposed record resolves within protocol limits. Authentication also depends on which IP and envelope domain the sending platform actually uses.