Understanding Email Risk Scores - MoltSets API Documentation

Why you might see more “invalid” results from other tools

In spring 2026, Microsoft began blocking SMTP-based email validation checks. Because of this, third-party validation vendors (NeverBounce, ZeroBounce, and others) have started marking fully configured, deliverable inboxes as “invalid” — even though these addresses can receive mail and should be sent to.

How MoltSets addresses this

To keep things transparent, MoltSets assigns every email an Email Risk Score. This score reflects what we actually know about deliverability, rather than relying solely on SMTP checks that are increasingly unreliable.

Score	What it means	Recommendation
A	Valid — known reply, open, or click	Send
B	Known send with no bounce	Probably send
C	Catch-all	Your call
D	Hard invalid — bounce, complaint, or spam trap	Don’t send
F	No data available	Your call

How it works

The Email Risk Score is appended to each record in the API payload. You retain full control over which emails to send to based on this score and your own risk tolerance.

Best Practices for Using Email Risk Scores

Treat the grade as a filter, not a guarantee. A “Send” recommendation lowers risk, it doesn’t eliminate it. Always pair risk scores with your own sending domain reputation and list hygiene practices.

By Grade

Grade	Best Practice
A	Safe to send to immediately. Strongest engagement signal available.
B	Solid to include in regular sends. For reputation-sensitive campaigns (e.g. cold outreach on a new domain), consider a smaller batch size before scaling up.
C	Deliverability can’t be confirmed. Segment separately from A/B, warm with lower volume, watch engagement closely, and suppress non-responders after 1-2 attempts.
D	Never send. Fastest way to trip spam traps and damage sender reputation for the whole list.
F	Treat as unknown risk, not safe. Re-verify before sending, or route into the same cautious treatment as C.

General Sending Hygiene

Suppress D scores automatically at the list level rather than relying on manual review
Monitor bounce rate by grade over time to validate the scoring is holding up for your specific use case
If sending cold outreach, warm up new domains regardless of score tier
Re-score contacts periodically; email validity decays over time (job changes, inbox closures)