MailerSend API
67
AI ReadinessAI-Aware (B)67/100
Official vendor OpenAPI document · agent-readyCommunicationsEmail Deliverybearer5 EndpointsREST
For Agents
Send transactional email - single or bulk - and pull per-domain activity reports through five endpoints with bearer-token auth.
Use for: Send a transactional welcome email to user@example.com via MailerSend, Submit a bulk batch of 50 password-reset emails in a single request, Get the bulk-email status for batch id abc123 to confirm completion, Find all bounce activity for the domain example.com in the last 24 hours
Not supported: Does not send SMS, manage marketing campaigns, or run subscriber lists - use for transactional email delivery only.
MailerSend is a transactional email delivery API designed for product and notification email at scale. The five-endpoint surface in this spec covers single-email send, bulk-email send with status polling, and per-domain or per-activity activity reporting. Authentication is a bearer API token issued from the MailerSend dashboard.
Install Jentic One Beta
Connect the MailerSend API to your agent
Jentic One is a self-hosted execution layer for AI agents. It lets your agent call the MailerSend API, or any other public or private API you need. You set the rules, the agent never sees your credentials, and every call is logged.
Two steps, two machines. Install the instance in a safe environment, then register your agent from wherever it runs.
1
Step 1: Jentic One Host machine
# On the machine that will host your Jentic One instance:
curl -fsSL "https://jentic.com/install.sh?src=apis&api=%2Fapis%2Fmailersend.com%2Fmailersend" | sh2
Step 2: Agent machine
# On the machine where your agent runs (keep this separate from the instance):
curl -fsSL "https://jentic.com/install.sh?src=apis&api=%2Fapis%2Fmailersend.com%2Fmailersend" | sh
jentic register # connects your agent to your Jentic One instanceJentic One is in public beta. The setup above keeps your agent separate from the instance, which is what you want before using real credentials: an agent running as the same OS user as Jentic One can read its stored keys directly. Just evaluating? A single local install is fine to start. See the secure deployment guide for the tiers.
Capabilities
What an agent can do with MailerSend API.
Send a single transactional email through POST /email
Submit a bulk-email batch through POST /bulk-email and poll status
Pull per-domain activity (delivered, opened, clicked, bounced) for analytics
Inspect a specific activity event by id for webhook reconciliation
Operate against the v1 base URL with bearer token auth
Use Cases
Patterns agents use MailerSend API for, with concrete tasks.
★ Transactional Email from a SaaS App
Send signup confirmations, password resets, and notification emails from a product backend by calling POST /email with from, to, subject, and html fields. MailerSend handles MTA queuing, bounce processing, and IP reputation, so the backend only needs to construct the message and submit it. A single call typically returns a queued status within sub-second latency.
POST /email with from=hello@app.com, to=[{"email":"jane@example.com"}], subject="Welcome", and an html body, then verify the response includes a x-message-id header.
Bulk Notification Batches
Send up to several thousand notifications in a single POST /bulk-email call rather than firing one HTTP request per recipient. The returned bulk_email_id can be polled through GET /bulk-email/{bulkEmailId} to confirm full completion before the orchestrator marks the job done. This is the right pattern for daily digest emails or a one-off blast to a known list.
POST /bulk-email with a JSON array of 100 messages, then poll GET /bulk-email/{bulkEmailId} every 5 seconds until status is completed.
Activity Reconciliation
Reconcile MailerSend webhook events with the API by calling GET /activity/{domainId} for a domain or GET /activities/{activityId} for a specific event. Use this when an event might have been missed by a webhook listener or to backfill an analytics warehouse with delivered, opened, and clicked counts.
Call /activity/{domainId} for the last 24 hours, filter for events with type=hard_bounced, and write each into a Postgres bounces table.
Agent-Driven Operational Mail
An AI agent that handles incidents or operational workflows can send a structured email to an on-call rotation through MailerSend via Jentic, then poll activity to confirm delivery before closing the ticket. The bearer token sits in your Jentic One instance, so the agent can be safely granted send rights without exposing credentials.
Send an incident summary email via POST /email to the on-call alias, then poll /activities/{activityId} until status is delivered before resolving the ticket.
Key Endpoints
5 endpoints — mailersend is a transactional email delivery api designed for product and notification email at scale.
METHOD
PATH
DESCRIPTION
POST
Send a transactional email
POST
/bulk-email
Submit a bulk-email batch
GET
/bulk-email/{bulkEmailId}
Get bulk-email batch status
GET
/activity/{domainId}
List activities for a domain
GET
/activities/{activityId}
Get a single activity event
POST/email
Send a transactional email
POST
/bulk-email
Submit a bulk-email batch
GET
/bulk-email/{bulkEmailId}
Get bulk-email batch status
GET
/activity/{domainId}
List activities for a domain
GET
/activities/{activityId}
Get a single activity event
Jentic AI Readiness Score
This API is usable in Jentic One now. Its AI-readiness score against Jentic's framework shows where it stands today and where improvements would make it even easier for agents to use.
M
MailerSend API
- AI-Aware (B)67/100
100
Foundational Compliance63
Developer Experience & Jentic Compatibility47
AI-Readiness & Agent Experience94
Agent Usability60
Security75
AI DiscoverabilityPowered by JenticScoring Framework 1.0.0 | Scoring Engine 0.4.0
Show dimension breakdown
100
Foundational Compliance
Base layer of spec validity and structural soundness.
Grade: A+Signals: 4
99%
Lint Results
Aggregated quality score from linter diagnostics, weighted by severity.
100%
Resolution Completeness
Percentage of `$ref` references that resolve successfully.
100%
Specification Validity
Checks whether the API description parses successfully and conforms to its declared specification (e.g., OpenAPI).
100%
Structural Integrity
Structural correctness score based on schema issues using logarithmic dampening.
63
Developer Experience & Jentic Compatibility
Clarity, completeness, and ingestion readiness for developers and tooling.
Grade: B-Signals: 4
0%
Example Density
How richly the API is illustrated with examples.
100%
Example Validity
Percentage of examples that conform to their schemas.
50%
Response Coverage
Percentage of operations with complete response definitions (success, client error, server error).
100%
Tooling Readiness
Health of API ingestion, bundling, and resolution within Jentic pipelines.
47
AI-Readiness & Agent Experience
Semantic breadth, depth, and agent comprehension for AI systems.
Grade: D+Signals: 4
40%
Description Coverage
Coverage of descriptions across API elements.
0%
Error Standardization
Coverage of RFC 9457 Problem Details for error responses.
100%
OperationId Quality
Coverage, uniqueness, and casing consistency of operationIds for AI inference.
50%
Summary Coverage
Coverage of summaries across operations/tags/info.
94
Agent Usability
Functional utility, complexity comfort, and AI orchestration readiness.
Grade: A+Signals: 1
94%
Complexity Comfort
Agent comfort level based on API operational and structural complexity.
60
Security
Trust, risk posture, and security compliance.
Grade: B-Signals: 1
60%
Authentication Strength
Average quality of security schemes based on authentication method strength (weakest link for OAuth2).
75
AI Discoverability
Findability, semantic richness, and reasoning readiness.
Grade: A-Signals: 1
75%
Descriptive Richness
Clarity and depth of descriptions across API elements.
Score it yourself
Every API in the directory is allowlisted, so you can re-score it with no key required.
npx @jentic/api-scorecard-cli score <openapi-url>Why Jentic?
What agents get from Jentic-routed access to this vendor.
Setup
Wiring the MailerSend API by hand means managing its bearer token, targeting the api.mailersend.com host, and handling its send and activity endpoints yourself. Through Jentic you install once, import MailerSend from the API Directory, store the token once, and your agent calls it.
Permission scoping
MailerSend carries the message recipients in the request body for sends, so limit the agent to the operations it needs, such as reading bulk-email status or activity, and add the send operation only when you want it. Every operation the agent can call is one you chose.
Credential isolation
Your MailerSend API token is stored once, encrypted, by your own Jentic One instance and injected at execution time. It never enters the agent's prompt, logs, or context.
Intent-based discovery
Agents search Jentic by intent such as 'send a transactional email' or 'check delivery activity', and Jentic returns the matching MailerSend operation with its input schema so the agent calls the right endpoint without browsing the reference docs.
Related APIs
Alternatives and complements available in the Jentic catalogue.
FAQs
Specific to using MailerSend API through Jentic.
What authentication does the MailerSend API use?
MailerSend uses bearer token authentication via the bearerAuth scheme. Generate the token from the MailerSend dashboard and send it in the Authorization header as Bearer {token}. Through Jentic the token is stored encrypted in the vault and injected at execution time.
Can I send bulk email in one request?
Yes. POST /bulk-email accepts an array of message objects and returns a bulk_email_id you poll via GET /bulk-email/{bulkEmailId} until status is completed. This is the right pattern for daily digests or one-off blasts to a known list.
What are the rate limits for the MailerSend API?
Rate limits depend on your MailerSend plan tier and are published at developers.mailersend.com. The default tier allows several thousand requests per hour. The OpenAPI spec does not encode the per-second cap, so watch for 429 responses and back off.
How do I send a transactional email through Jentic?
Search Jentic for "send a transactional email" and load POST /email. Execute with from, to, subject, and html fields populated. The response includes a x-message-id header you can correlate with /activities/{activityId}.
Is the MailerSend API free?
MailerSend includes an API quota on the free plan (currently 3000 emails per month). Higher plans raise the monthly cap and unlock advanced features such as dedicated IPs and a higher bulk-email batch size.
Can I limit what my agent is allowed to do with the MailerSend API?
Yes. Because you run your own self-hosted Jentic One instance, your own rules decide which MailerSend operations the agent may call. You can grant read-only access to GET /bulk-email/{bulkEmailId}, GET /activity/{domainId}, and GET /activities/{activityId} for status and reporting, and add the sending operations POST /email or POST /bulk-email only when you want the agent to dispatch mail. Every operation the agent can reach is one you chose, and the bearer token is injected at execution time rather than exposed to the agent.
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