Errors or Stops while sending emails

If the program encounters an error or stops while sending emails, consider increasing the Sleep value in the Program Settings. Since this value is measured in milliseconds, try raising it by 1000 to see if that resolves the issue.

Some SMTP servers may become overwhelmed when too many emails are sent consecutively.

If you are using Exchange Server

You may be hitting your Exchange server’s message submission rate limit.

Why the Error Happens

• Exchange applies message throttling to prevent a single client or application from overwhelming the server.
• The default MessageRateLimit is often set low (e.g., 5–20 messages per minute per client).
• If an application or script sends more than this threshold, Exchange rejects further submissions with the error:
  “421 4.4.2 Message submission rate for this client has exceeded the configured limit.”.

How to Fix It

1. Check Current Limits

Run this in Exchange Management Shell:

Get-ReceiveConnector | ft Name, MessageRateLimit

This shows the configured limits for each connector.

2. Increase the Limit

Identify the connector your client uses (often Default or Client ), then raise the limit:

Set-ReceiveConnector -Identity "Default " -MessageRateLimit 200

• Replace 200 with a value appropriate for your workload.
• You can also set -MessageRateLimit unlimited if you want no restriction, but this is risky unless you fully trust the sending application.

3. Consider MessageRateSource

Exchange can enforce limits per user, IP, or connector. If your app uses a single account, it may hit the limit faster. Splitting traffic across accounts or adjusting MessageRateSource can help.

4. Application Design

If you’re sending bulk or automated mail:

• Throttle your app: Add delays or batching so you don’t exceed the per‑minute threshold.
• Use a dedicated mailer: Exchange is not ideal for bulk email; consider an external SMTP service for high‑volume campaigns.

Best Practices

Coordinate with IT policy: Some organizations deliberately keep limits low to prevent abuse.

Don’t disable limits entirely unless you’re certain the sender is safe. Limits protect against runaway processes and spam.

Monitor logs: Use message tracking logs to confirm which account or connector is hitting the limit.