Sendmux Token Efficient Usage

Sendmux token-efficient usage

Use this skill to choose the lowest-cost Sendmux route that still answers the task correctly.

Boundaries

• Do not ask the user to paste an API key.
• Use send-capable smx_mbx_* keys or owner-approved Sending-resource smx_agent_* tokens for Sending calls, and smx_mbx_* keys for normal Mailbox calls.
• Use scoped smx_agent_* only for the calls its scopes and resource allow. Pre-claim agent tokens cannot send.
• Use smx_root_* for Management calls.
• Do not default to MCP for every task. MCP is best when the required tool is curated; CLI and SDK cover broader surfaces.
• Do not pipe real attachments through model context as base64. Route attachment transfer to sendmux-attachments; prefer file_path, presigned URLs, CLI --attach, or SDK file helpers. Mailbox uploads cap each attachment at 7,500,000 bytes; Sending uploads cap each file at 18 MiB; MCP inline base64 caps at 32 KiB decoded.
• Do not read full mailbox bodies, every message, or every log row unless the user asks for full content and narrower calls cannot answer.

Surface choice

Cheapest-call map

Read less

For mailbox questions, reduce the result set before reading content:

1. Count when the user asks "how many" or when the query may be broad.
2. Search snippets with a small limit when the user needs examples.
3. Batch-get only selected message IDs.
4. Request clean body/content only when message text affects the answer.

CLI:

sendmux mailbox:count-messages \
  --query q=invoice \
  --query is_unread=true \
  --json

sendmux mailbox:search-message-snippets \
  --query q=invoice \
  --query is_unread=true \
  --query limit=10 \
  --json

sendmux mailbox:batch-get-messages \
  --body '{
    "ids": ["eml_abc", "eml_def"],
    "body_mode": "clean_json",
    "max_body_chars": 4000,
    "strip_quotes": true,
    "strip_signature": true,
    "include_attachments": "metadata"
  }' \
  --json

Write fewer requests

Batch when there is more than one target.

sendmux sending:send:batch \
  --idempotency-key "$IDEMPOTENCY_KEY" \
  --body-file ./messages.json \
  --json

sendmux mailbox:batch-update-messages \
  --body '{
    "ids": ["eml_abc", "eml_def"],
    "seen": true,
    "if_in_state": "state_from_prior_read"
  }' \
  --json

For batch sends, inspect every per-message result before reporting success. Batch can contain mixed outcomes.

Sync by delta

Use sync endpoints instead of re-listing stable data.

Broad mailbox sync:

sendmux mailbox:get-changes \
  --query messages_since_state="$MESSAGES_STATE" \
  --query folders_since_state="$FOLDERS_STATE" \
  --query threads_since_state="$THREADS_STATE" \
  --query limit=100 \
  --json

Filtered message sync:

sendmux mailbox:query-message-changes \
  --query since_query_state="$QUERY_STATE" \
  --query q=invoice \
  --query is_unread=true \
  --query limit=100 \
  --json

Store the returned state token. Continue with the same filters only while has_more is true and the next page is needed.

Transfer less

• Use small limit values on list calls.
• Follow pagination.next_cursor only until enough evidence has been gathered.
• Prefer summary or metrics endpoints before log lists.
• Use If-None-Match for repeated detail reads that previously returned an ETag.
• Use If-Match for updates when the prior read returned an ETag.
• For inbound attachments, fetch metadata and use the short-lived download_url; if it expires, re-fetch metadata instead of building URLs manually.
• For outbound attachments, a file path or presigned URL is usually under 100 tokens, while base64 can burn thousands of tokens and corrupt large files.

CLI conditional examples:

sendmux management:get-email-log \
  --path public_id=dlog_abc \
  --if-none-match "$ETAG" \
  --json

sendmux management:update-mailbox \
  --path public_id=mbx_abc \
  --if-match "$ETAG" \
  --body '{"display_name":"Agent Inbox"}' \
  --json

SDK helpers:

import {
  conditionalHeaders,
  idempotencyHeaders,
  paginate,
  responseEtag,
} from "@sendmux/core";

const headers = conditionalHeaders({ ifNoneMatch: priorEtag });
const writeHeaders = {
  ...conditionalHeaders({ etag: priorEtag }),
  ...idempotencyHeaders(operationKey),
};

Retry safely

Use Idempotency-Key on supported mutations so retrying does not create duplicate work.

Good candidates:

• sending:send and sending:send:batch.
• mailbox:send-message.
• Management creates, mailbox key creation, suspend/resume, provider mutations, webhook create/rotate/test.

When retrying application code, prefer SDK retry helpers only for safe reads or idempotent writes. Non-idempotent writes should fail rather than risk duplicate side effects.

Routing

• Setup, key scopes, first call: sendmux-getting-started.
• Email send bodies and SMTP-vs-HTTP choice: sendmux-send-email.
• Attachment upload/download mechanics: sendmux-attachments.
• Mailbox read/search/sync/triage/reply details: sendmux-mailbox-agent.
• Management domains, mailboxes, webhooks, billing, logs: sendmux-management.
• CLI syntax and profiles: sendmux-cli.
• MCP installation and client config: sendmux-mcp-setup.