Lettr MCP Server
lettr-mcp
npm
v1.5.0
Source verified
Published by lettr-com — publish provenance cryptographically ties this package to that repository. That is proof of origin, not an official vendor package.
MCP server for the Lettr email API — send transactional emails, manage templates, domains, and webhooks from any AI assistant
The grade answers one question — how safe is this server for you to adopt — so it is computed in two auditable stages. Nothing below is an opinion or an LLM's guess; every line is a real term the deterministic engine applied, and the same input always yields the same number.
1. Threat score — 100 − 0 = 100. What the published surface and source actually contain:
The deterministic scan raised no scored threat in the surface it inspected — the threat score stayed at 100. Capability observations and advisory notes are recorded but never lower it.
2. Client adoption risk — 100 − 6 = 94. Three small, subtract-only factors that reflect your risk in adopting it — a clean scan proves less on a powerful, unverified or barely-inspectable package, so the grade says so plainly:
| Points | Adoption-risk factor |
|---|---|
| −6 | capability blast radius (high) — client exposure if the model is manipulated |
Capability observations and info notes are shown under Findings but never scored.
Open any row's finding below for the file, line and evidence behind a deduction.
Findings 7
high Read-and-egress in one tool: "create-webhook"MTC-FLOW-003
Tool "create-webhook" can both read sensitive data and send data to an external destination. Even without an explicit untrusted-input leg, this is a single-call data-exfiltration path if the model is ever manipulated.
Fix: Separate reading from sending; require explicit user confirmation before egress of file/secret contents.
Location: flow create-webhook
high Read-and-egress in one tool: "update-webhook"MTC-FLOW-003
Tool "update-webhook" can both read sensitive data and send data to an external destination. Even without an explicit untrusted-input leg, this is a single-call data-exfiltration path if the model is ever manipulated.
Fix: Separate reading from sending; require explicit user confirmation before egress of file/secret contents.
Location: flow update-webhook
high Sensitive-source and external-sink co-existMTC-FLOW-004
Tools that read sensitive data ([create-webhook, update-webhook]) and tools that can send data out ([send-email, schedule-email, create-webhook, update-webhook, delete-webhook]) are exposed together. An agent can move private data to the sink.
Evidence: sources [create-webhook, update-webhook] → sinks [send-email, schedule-email, create-webhook, update-webhook, delete-webhook]
Fix: Keep secret-reading and egress capabilities on separate, separately-approved servers.
Location: flow create-webhook → send-email
medium Unconstrained URL/host parameter "url" on "create-webhook"MTC-CAP-007
Tool "create-webhook" takes a URL/host parameter "url" with no allowlist/pattern. An outbound-request tool with an unbounded destination enables SSRF and cloud-metadata access (e.g. 169.254.169.254).
Fix: Allowlist destinations or constrain the parameter; block private/link-local addresses server-side.
Location: tool create-webhook · inputSchema.properties.url
medium Unconstrained URL/host parameter "oauth_token_url" on "create-webhook"MTC-CAP-007
Tool "create-webhook" takes a URL/host parameter "oauth_token_url" with no allowlist/pattern. An outbound-request tool with an unbounded destination enables SSRF and cloud-metadata access (e.g. 169.254.169.254).
Fix: Allowlist destinations or constrain the parameter; block private/link-local addresses server-side.
Location: tool create-webhook · inputSchema.properties.oauth_token_url
medium Unconstrained URL/host parameter "url" on "update-webhook"MTC-CAP-007
Tool "update-webhook" takes a URL/host parameter "url" with no allowlist/pattern. An outbound-request tool with an unbounded destination enables SSRF and cloud-metadata access (e.g. 169.254.169.254).
Fix: Allowlist destinations or constrain the parameter; block private/link-local addresses server-side.
Location: tool update-webhook · inputSchema.properties.url
medium Unconstrained URL/host parameter "oauth_token_url" on "update-webhook"MTC-CAP-007
Tool "update-webhook" takes a URL/host parameter "oauth_token_url" with no allowlist/pattern. An outbound-request tool with an unbounded destination enables SSRF and cloud-metadata access (e.g. 169.254.169.254).
Fix: Allowlist destinations or constrain the parameter; block private/link-local addresses server-side.
Location: tool update-webhook · inputSchema.properties.oauth_token_url
Tools 68
Each tool and what it can reach — statically extracted from the published source.
create-webhooknetwork egressreads sensitive dataupdate-webhooknetwork egressreads sensitive datadelete-webhooknetwork egressschedule-emailnetwork egresssend-emailnetwork egressattach-contact-to-listno sensitive capabilityauth-checkno sensitive capabilitybulk-attach-contacts-to-listsno sensitive capabilitybulk-create-audience-contactsno sensitive capabilitybulk-delete-audience-listsno sensitive capability
Show 58 more tools ↓
bulk-detach-contacts-from-listsno sensitive capabilitybulk-subscribe-contacts-to-topicsno sensitive capabilitybulk-unsubscribe-contacts-from-topicsno sensitive capabilitycancel-scheduled-emailno sensitive capabilitycreate-audience-contactno sensitive capabilitycreate-audience-listno sensitive capabilitycreate-audience-propertyno sensitive capabilitycreate-audience-segmentno sensitive capabilitycreate-audience-topicno sensitive capabilitycreate-domainno sensitive capabilitycreate-templateno sensitive capabilitydelete-audience-contactno sensitive capabilitydelete-audience-listno sensitive capabilitydelete-audience-propertyno sensitive capabilitydelete-audience-segmentno sensitive capabilitydelete-audience-topicno sensitive capabilitydelete-domainno sensitive capabilitydelete-templateno sensitive capabilitydetach-contact-from-listno sensitive capabilityget-audience-contactno sensitive capabilityget-audience-listno sensitive capabilityget-audience-propertyno sensitive capabilityget-audience-segmentno sensitive capabilityget-audience-topicno sensitive capabilityget-campaignno sensitive capabilityget-domainno sensitive capabilityget-email-detailno sensitive capabilityget-merge-tagsno sensitive capabilityget-scheduled-emailno sensitive capabilityget-templateno sensitive capabilityget-template-htmlno sensitive capabilityget-webhookno sensitive capabilityhealth-checkno sensitive capabilitylist-audience-contactsno sensitive capabilitylist-audience-listsno sensitive capabilitylist-audience-propertiesno sensitive capabilitylist-audience-segmentsno sensitive capabilitylist-audience-topicsno sensitive capabilitylist-campaign-eventsno sensitive capabilitylist-campaignsno sensitive capabilitylist-domainsno sensitive capabilitylist-email-eventsno sensitive capabilitylist-emailsno sensitive capabilitylist-projectsno sensitive capabilitylist-templatesno sensitive capabilitylist-webhooksno sensitive capabilityschedule-campaignno sensitive capabilitysend-campaignno sensitive capabilitysubscribe-contact-to-topicno sensitive capabilityunschedule-campaignno sensitive capabilityunsubscribe-contact-from-topicno sensitive capabilityupdate-audience-contactno sensitive capabilityupdate-audience-listno sensitive capabilityupdate-audience-propertyno sensitive capabilityupdate-audience-segmentno sensitive capabilityupdate-audience-topicno sensitive capabilityupdate-templateno sensitive capabilityverify-domainno sensitive capability
Toxic flows 3
Cross-tool combinations that form a data-exfiltration primitive (untrusted input → sensitive source → external sink).
What this scan could not see
- Tools were statically extracted from the published source (68 recovered), not enumerated from a running server. Tool-poisoning, Unicode-smuggling, capability and toxic-flow analysis ran on this inferred surface, but a mis-parsed registration could be missed or mis-attributed, so tool-derived findings are capped below “confirmed”. To grade the real runtime surface, scan the running server: --command "npx -y <package>".
Versions 2
Scan history per published version. The engine is deterministic — the same version always yields the same score, so a changed score means the package itself changed.
| Version | Score | Findings | Engine | Scanned |
|---|---|---|---|---|
v1.5.0 latest |
A 94/100 | 7 | 1.13.0 | 2026-09-07 |
v1.4.0 |
A 94/100 | 7 | 1.12.1 | 2026-08-15 |
Embed this score
Show this server's live Trust Score in your README, docs or website. The badge is served straight from the registry and updates automatically after every rescan — no API key needed. It links back to this page, so anyone who sees the grade can also read the findings behind it instead of taking a number on faith.
Verify this score yourself
The score above is reproducible: the same package version always yields the same result. Run it locally or over the free API — no account, no LLM, fully deterministic.
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