established · 2.3 marketcapability domainresource

SMTP

Score 24.5 / 100 25 providers 8 APIs Search apis.io →
Variants seen in the corpus: SMTPsmtp

Providers using this tag (25)

Ranked by API Evangelist rating — Exemplar and Strong are expanded by default.

Exemplar 9 Complete, well-documented, and agent-ready
HubSpotAnalyticsCommerceContentCRM93 APIs82.4Amazon SESEmailEmail DeliverabilityEmail ServiceMarketing Email17 APIs79.7SendGridEmailEmail APIMarketing Email63 APIs77.0SendPulseMarketingMarketing AutomationEmailTransactional Email19 APIs75.7SMTP2GOEmailEmail DeliveryTransactional Email11 APIs73.6MailboxlayerEmailEmail VerificationEmail Validation2 APIs73.4PostmarkEmailsMessagingTransactional EmailDeliverability47 APIs71.1MailosaurEmail TestingSMS TestingDeveloper ToolsQA Automation7 APIs71.0MoosendEmail MarketingMarketing AutomationCampaignsMailing Lists1 API67.9
Strong 3 Solid coverage with minor gaps
MailerSendEmailTransactional EmailMarketing8 APIs64.6SmartleadCold EmailOutboundSalesDeliverability11 APIs63.6AgentMailCompanyArtificial IntelligenceEmailAI Agents28 APIs54.7
Developing 5 Usable, with meaningful gaps to close
AhaSendEmailTransactional EmailDeveloper Tools11 APIs49.2uCheckerEmail VerificationEmailDNS3 APIs48.0Pure StorageStorageData StorageFlash StorageEnterprise Storage130 APIs45.0SparkPostEmailTransactional EmailMarketing EmailEmail Delivery12 APIs43.9Apache JamesEmailIMAPJavaJMAP9 APIs39.8
Thin 6 Limited public surface area
MailjetEmailEmail DeliveryMarketing Email8 APIs38.9ZohoAnalyticsCollaborationCRMCustomer Service34 APIs38.5MailerooEmailEmail DeliveryMarketing Email2 APIs36.7MailPaceEmailTransactional EmailMessaging4 APIs35.6MailgunEmailTransactional EmailEmail Validation8 APIs34.0EmailEngineEmailEmail APIIMAP13 APIs30.5
Emerging 1 Early or largely undocumented
SMTPEmailInternet StandardsIETF2 APIs14.0
Minimal 1 Almost no public developer surface
PostfixEmailMail ServerMTA1 API9.9

APIs with this tag (8)

Ranked by the provider's API Evangelist rating — the Kin Score is scored per provider, not per API, so every API of a provider shares its band. How the rating works →

Exemplar 3 Complete, well-documented, and agent-ready
HubSpot Transactional Email APIThe transactional email API enables sending template-based transactional emails through HubSpot using the S...82.4SendPulse SMTP APITransactional email sending, delivery and bounce tracking, unsubscribe management and sender-domain identity.75.7SMTP2GO Email APIREST API for sending transactional emails and SMS, managing sender domains, SMTP users, API keys, templates...73.6
Strong 1 Solid coverage with minor gaps
Smartlead Email Accounts APIEndpoints to add, list, update, and remove sender mailboxes (SMTP, Gmail, Outlook), assign them to campaign...63.6
Developing 1 Usable, with meaningful gaps to close
Pure Storage SMTP APIManages Simple Mail Transfer Protocol (SMTP) settings. SMTP allows the array to send email notifications an...45.0
Thin 1 Limited public surface area
Zoho ZeptoMailThe Zoho ZeptoMail API provides REST endpoints for sending transactional emails such as OTPs, password rese...38.5
Emerging 1 Early or largely undocumented
RFC 5321 - Simple Mail Transfer ProtocolRFC 5321 is the IETF standard defining the Simple Mail Transfer Protocol. It specifies the client-server pr...14.0
Minimal 1 Almost no public developer surface
Postfix SMTPPostfix implements SMTP (RFC 5321) for sending and receiving electronic mail, with submission (port 587), S...9.9

Score breakdown

Frequency
40.5
log-scaled weighted occurrences
Breadth
0.7
spread across providers
Quality lift
64.0
mean composite of providers using it
Cohesion
9.1
strength of nearest seed neighbor

Related tags

Transactional Email 15 co-occurrences Deliverability 11 co-occurrences Email Delivery 6 co-occurrences Marketing Email 5 co-occurrences Email 21 co-occurrences Domains 7 co-occurrences Templates 9 co-occurrences Message 6 co-occurrences

Where this tag comes from

Provider tag20
Api tag8
Openapi tag1
Openapi op tag4

Cohort brief

Auto-generated

The 25 providers in the APIs.io catalog tagged SMTP, scored on the Kin Score. Every figure below is computed from the catalog — nothing here is written.

Providers
25
all scored
Mean Kin Score
52.7
+32.0 vs catalog 20.7
Mean Agent Readiness
31.2
+21.5 vs catalog 9.7
Spread
9.9–82.4
median 49.2 · σ 20.2
How the 25 split by band
Exemplar 9Strong 3Developing 5Thin 6Emerging 1Minimal 1
Facet averages, against the whole catalog
FacetThis cohortCatalogDifferenceScored
Access Clarity 61.4 22.3 +39.1 25
Contract Quality 55.4 17.5 +37.9 25
Developer Ergonomics 53.1 17.9 +35.2 25
Operational Transparency 40.2 11.3 +28.9 25
Contract Governance 21.6 6.4 +15.2 25
Discoverability 75.5 60.4 +15.1 25

A facet is averaged over the members that carry it, not over the whole cohort — the “Scored” column is that count. Averaging an absent facet as zero would score our own coverage gaps as the providers’ posture.

What this cohort publishes
ArtifactThis cohortCatalogDifference
MCP server (any) 52% 16% +36
MCP server (first-party) 40% 7% +33
Agent Skills 0% 0% 0
OAuth scopes 16% 9% +7
Security 100% 88% +12
Arazzo workflows 8% 2% +6
Governance rules 48% 13% +35

mcp_pct counts any mcp/ artifact including ones API Evangelist derived from the provider OpenAPI; mcp_first_party_pct counts only servers the provider publishes. Prefer the latter.

Top by Kin Score
  1. 1 HubSpot 82.4
  2. 2 Amazon SES 79.7
  3. 3 SendGrid 77
  4. 4 SendPulse 75.7
  5. 5 SMTP2GO 73.6
  6. 6 Mailboxlayer 73.4
  7. 7 Postmark 71.1
  8. 8 Mailosaur 71
  9. 9 Moosend 67.9
  10. 10 MailerSend 64.6
Top by Agent Readiness
  1. 1 SendPulse 55.8
  2. 2 HubSpot 54.4
  3. 3 MailerSend 50.2
  4. 4 AgentMail 45.7
  5. 5 Amazon SES 41.6
  6. 6 SendGrid 41.2
  7. 7 SMTP2GO 39.4
  8. 8 Postmark 38.7
  9. 9 Smartlead 38
  10. 10 uChecker 36.7
All 25 members of this roster resolve to a scored provider in the catalog.Generated from the catalog build of 25 August 2026, across 26891 providers, using the same computation served by the APIs.io cohort API. Briefs are published for rosters of 5 or more scored providers; below that a distribution is not meaningful.

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Tools for tags

7 MCP tools reach this
  • find_tagsBrowse and filter every tag in the catalog.
  • get_cohortThis tag as a scored cohort — every provider carrying it, with scores.
  • cohort_statsPRO — the distribution across this tag: mean, median, band split, adoption rates.
  • cohort_rankingsPRO — the leaderboard, on composite AND agent-readiness axes.
  • apis_io_searchSTART HERE — APIs, providers and tags for one query, each with its total.
  • resolveTurn a domain, URL or GitHub org into the provider it belongs to.
  • find_cohortsEvery scored population of providers in the catalog.
All 92 tools

Call it yourself

curl for this page
This tag 
curl "https://apis.io/api/v1/tags/smtp"
All tags 
curl "https://apis.io/api/v1/tags?limit=25"
As a scored cohort 
curl "https://apis.io/api/v1/cohorts/tag/smtp"
The distribution (Pro) 
curl "https://apis.io/api/v1/cohorts/tag/smtp/stats" \
  -H "X-API-Key: $APIS_IO_KEY"

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