# Choosing an outbound callout mechanism

*Integration Architect Study Guide · Build Solution · Last updated October 16, 2026 · https://www.certifyforce.com/study-guide/integration-architect/build-solution/choosing-an-outbound-callout-mechanism*

How to pick the way Salesforce calls out: named credential endpoints and the callout: scheme, synchronous versus Queueable, future and platform event subscribers, callouts after uncommitted DML, async request plus callback for long jobs, outbound message versus platform event delivery, Event Relay to Amazon EventBridge, Flow HTTP Callout limits and Named Principal versus Per User identity.

- Certification: Salesforce Integration Architect
- Exam section: Build Solution
- Study guide: https://www.certifyforce.com/study-guide/integration-architect

**Official exam objective:**

> Given a use case, identify the considerations when choosing the right option in making an outbound call to an external system.

## What the exam expects

- Choose the outbound mechanism from the requirement: does a user wait for the answer, how long does the remote work take, and what does the target accept?
- Point callouts at named credentials, reuse one credential across resource paths, and pick Named Principal or Per User identity.
- Avoid callouts after uncommitted DML and in front of users when a partner throttles; pick Queueable, future or a platform event subscriber.
- Contrast outbound message and platform event delivery, and know when Event Relay or Flow HTTP Callout fits.

Key terms: **named credential** (endpoint URL plus a reference to an external credential holding authentication); **`callout:` URL** (the scheme Apex uses to reference a named credential); **Named Principal / Per User** (one shared identity versus each user's own credential); **Event Relay** (low-code stream of events to Amazon EventBridge); **callback** (the remote system calls Salesforce back when its work finishes).

## Key facts

| Fact | Detail | Source |
|---|---|---|
| Endpoint authorization | Remote Site Settings required unless the endpoint is a named credential | [Invoking Callouts Using Apex](https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_callouts.htm) |
| Named credential URL | `callout:Name/path?query`; path and query vary per request | [Named Credentials as Callout Endpoints](https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_callouts_named_credentials.htm) |
| Named Principal | One admin credential for all users | [Authentication Protocols](https://help.salesforce.com/s/articleView?id=sf.nc_auth_protocols.htm&type=5) |
| Pending work | No callout after DML, async Apex, scheduled Apex or email in the same transaction | [Callout Limits and Limitations](https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_callouts_timeouts.htm) |
| Continuation timeout | 120 seconds maximum | [Asynchronous Callout Limits](https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_continuation_limits.htm) |
| Future parameters | Primitives, arrays or collections of primitives only | [Future Methods](https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_invoking_future_methods.htm) |
| Queueable callouts | `Database.AllowsCallouts`; job ID from `System.enqueueJob` | [Queueable Apex](https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_queueing_jobs.htm) |
| Outbound message delivery | Salesforce retries until the endpoint acknowledges; 24-hour replay period | [Integration Patterns](https://architect.salesforce.com/docs/architect/fundamentals/guide/integration-patterns.html), [Event-Driven Architecture Decision Guide](https://architect.salesforce.com/docs/architect/decision-guides/guide/event-driven.html) |
| Platform event delivery | Published once, no Salesforce retry; replay within 72 hours | [Integration Patterns](https://architect.salesforce.com/docs/architect/fundamentals/guide/integration-patterns.html) |
| Event Relay target | Amazon EventBridge only | [Event-Driven Architecture Decision Guide](https://architect.salesforce.com/docs/architect/decision-guides/guide/event-driven.html) |

## Check yourself

- Why does a hard-coded endpoint fail with "Unauthorized endpoint" while a named credential works?
- When should an outbound integration use Event Relay?
- Why convert a future method to Queueable when the job must carry sObjects and be monitored?
- When does a remote job need a callback instead of a callout that waits?

## Sources

- [Integration Patterns](https://architect.salesforce.com/docs/architect/fundamentals/guide/integration-patterns.html)
- [Named Credentials as Callout Endpoints](https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_callouts_named_credentials.htm)
- [Invoking Callouts Using Apex](https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_callouts.htm)
- [Callout Limits and Limitations](https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_callouts_timeouts.htm)
- [Authentication Protocols for Named Credentials](https://help.salesforce.com/s/articleView?id=sf.nc_auth_protocols.htm&type=5)
- [Guidelines for Authenticating HTTP Callout Actions](https://help.salesforce.com/s/articleView?language=en_US&id=platform.flow_http_callout_guidelines_authenticating.htm&type=5)
- [Queueable Apex](https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_queueing_jobs.htm)
- [Future Methods](https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_invoking_future_methods.htm)
- [Optimize Queueable Apex for Asynchronous Processing](https://trailhead.salesforce.com/content/learn/modules/asynchronous_apex/async_apex_queueable)
- [Asynchronous Callout Limits](https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_continuation_limits.htm)
- [Reliability (Well-Architected)](https://architect.salesforce.com/docs/architect/well-architected/guide/reliability.html)
- [Data Integration Decision Guide](https://architect.salesforce.com/docs/architect/decision-guides/guide/data-integration.html)
- [Event-Driven Architecture Decision Guide](https://architect.salesforce.com/docs/architect/decision-guides/guide/event-driven.html)
- [Event Relay: Get Started](https://developer.salesforce.com/docs/platform/event-relay/guide/intro.html)
- [Named Credential Formula Functions](https://developer.salesforce.com/docs/platform/named-credentials/references/named-credentials-reference/nc-formula-functions.html)

## About the full unit

The "Core concepts", "Exam traps" and "Worked scenario" sections of this unit, its 11 linked practice questions, and unlimited timed mock exams are included with the Integration Architect pack (USD $19): https://www.certifyforce.com/practice-exams