Too many recipients
Production Risk
Medium — causes partial delivery failures in bulk sending if not handled.
The number of recipients specified in the RCPT TO commands exceeds the maximum number the receiving server allows per message transaction.
- 1The sending client issued more RCPT TO commands than the server's per-transaction recipient limit.
- 2A bulk mailer did not split large recipient lists into multiple transactions.
- 3The server has a conservative recipient limit for anti-spam purposes.
A client sends RCPT TO for more recipients than the server allows in a single transaction (commonly 100 or 500).
# After the 101st RCPT TO (server limit is 100): 452 5.5.3 Too many recipients
expected output
452 5.5.3 ...
Fix
Split recipient list into batches
WHEN Sending to large recipient lists
// Split recipients into chunks of 50 (conservative limit)
const BATCH_SIZE = 50;
for (let i = 0; i < recipients.length; i += BATCH_SIZE) {
const batch = recipients.slice(i, i + BATCH_SIZE);
await sendMessage({ to: batch, subject, body });
}Why this works
Sending in batches of 50-100 recipients per transaction stays well within most server limits.
✕ Add all recipients to a single SMTP transaction
Most servers enforce per-transaction recipient limits, typically between 100 and 500.
RFC 3463 — Enhanced Mail System Status Codes
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