Send Email Tool

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What it does

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Key features

• Send to one or multiple recipients in a single call
• Full HTML body support with inline styling, lists, tables, links
• Attach files from the conversation by filename — generated reports, CSVs, PDFs, anything produced by other tools
• Agent name is used as the display name automatically — different agents in the same org show as different senders
• Works with Resend BYO — when your org has a Resend connection, the tool uses your API key and verified domain transparently

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Parameters

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From-address behavior

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Common use cases

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Send a notification

to: ["user@example.com"]
subject: "Task Completed Successfully"
html: "<h2>Task Update</h2><p>Your data analysis task has been completed successfully. Please check the results in your dashboard.</p>"

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Send a report with an attached file

to: ["manager@company.com", "team@company.com"]
subject: "Weekly Sales Report"
html: "<h1>Weekly Sales Report</h1><p>Summary attached. Top-line numbers in the body.</p><ul><li>Total: $15,000</li><li>Top product: Product A ($8,000)</li></ul>"
attachment_filenames: ["weekly_sales_2026-06.xlsx"]

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Send an alert

to: ["admin@company.com"]
subject: "System Alert: High CPU Usage"
html: "<div style='color: red;'><h2>System Alert</h2><p>CPU usage has exceeded 90% for the past 10 minutes.</p></div>"

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Send a daily digest from a scheduled task

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HTML formatting tips

• Use standard inline HTML — <h1>, <h2>, <p>, <strong>, <em>, <a href="…">, <ul>, <ol>, <table>
• Prefer inline style="…" over <style> blocks — many email clients strip the latter
• Keep CSS simple; avoid flexbox/grid for layout (poor email-client support)
• Test on Gmail and Outlook for any high-volume sending

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Best practices

• Keep subject lines short and specific — recipients see them before the body
• For high-volume sending or external recipients, connect BYO Resend so your domain’s reputation is what carries deliverability
• For attachments, generate the file with execute_python or another tool earlier in the conversation, then reference it by exact filename
• Resend’s per-message attachment cap is 40 MB total across all attachments — oversize files are skipped with a warning rather than rejecting the whole send

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Troubleshooting

• The to parameter must be a non-empty array of strings (e.g. ["a@b.com"])

• Both subject and html are required and must be non-empty strings

• The from-address’s domain isn’t fully verified in Resend, the recipient is malformed, or the key was revoked — see Resend integration troubleshooting

• Email clients aggressively strip CSS — stick to inline styles and standard tags
• Use a litmus test recipient to preview before broad sends

• The attachment_filenames entry must match exactly the filename of a file already in the conversation (case-sensitive, including extension)
• Files generated by tools earlier in the conversation are referenceable by their filename — check the tool result for the exact filename it produced
• If the file is missing from the conversation, the tool logs a warning and proceeds without the attachment rather than failing the send

• Confirm Resend is connected under Control Hub > Integrations > Resend — the card should show Connected
• See the Resend integration troubleshooting for connection issues

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Related

• Resend Integration — connect your own Resend account so agents send from your verified domain
• Manage Scheduled Tasks — scheduled agents typically end with send_email to deliver a digest
• Run Code — generate report files in the conversation, then attach them via attachment_filenames
• Email Your Agent — let users email an agent and get an emailed reply back (uses the same outbound path, including BYO Resend)