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✉️ Email Delivery

Documentation, reference material and tutorials for CRM-NG SMTP Email: setup guides for every mail service, troubleshooting, and one article per error message.

Error: 442 Connection dropped during transmission

Updated

By Duane GarnerChief Executive Officer (CEO)
Summarize: Claude ChatGPT View Markdown
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The connection to the mail server broke while the message was being sent. Usually a network or server hiccup; retry, then look for a pattern.

Shown by SMTP-based sending (Other SMTP, Zoho Mail, the backup SMTP transport)

The test result or the error log shows a reply such as 442 The connection was dropped during the transmission or another message containing "connection dropped".

This article is for site owners sending through an SMTP server who see the connection break partway through a send.

What this error means

The connection to the mail server was open and the conversation had started, but it ended before the message was fully handed over. Code 442 is not one of the core SMTP reply codes; some servers use it to say exactly this. Because the code starts with 4, it is a temporary failure: the same message may well go through on the next try.

Since the message was cut off, the server did not accept it. It was not delivered.

Common causes

  • A short network interruption between your web server and the mail server.
  • The mail server closed the connection because it was overloaded or restarting.
  • The message took too long to transmit, for example a very large attachment on a slow link, and a timer on either side ran out.
  • A firewall, proxy or security appliance on the path cut connections it considered idle or suspicious.
  • The server dropped the connection because of a policy, such as too many messages in one session.

How to fix

  1. Try again

    Go to CRM-NG SMTP → Tools → Email Test, fill in Send To and press Send Email. A one-off drop usually clears on its own.

  2. Look for a pattern

    Open CRM-NG SMTP → Settings → Email Log and filter failed messages. If only large emails fail, attachments are the likely trigger. If failures cluster at certain times, the server or network may be busy then.

  3. Reduce message size

    If big attachments are involved, link to files instead of attaching them, or reduce their size.

  4. Check the connection settings

    Go to CRM-NG SMTP → Settings → General and confirm SMTP Host, SMTP Port and Encryption match the provider's recommended values. Save.

  5. Ask your host and mail provider

    If drops keep happening, share the error from CRM-NG SMTP → Tools → Debug Events with your web host and your mail provider and ask whether either side is cutting connections.

Verify it worked

The test page shows "Test email sent successfully! Check your inbox to confirm delivery." Over the next day the Email Log shows no new 442 failures.

Notes

  • Set up a backup SMTP transport on the Alerts tab so temporary failures on the main connection can be carried by a second route.
  • Optimize Email Sending on CRM-NG SMTP → Settings → Misc moves sending into the background, so a slow or dropped connection does not hold up your pages.
  • If drops are frequent and you use Other SMTP, an API mailer over HTTPS is often more reliable.
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