Summary
The error 'Server is not currently available, possibly due to too many connections' arises from exceeding recipient mail server connection limits or temporary server issues. The 421 SMTP error signifies a temporary service disruption. Solutions involve throttling sending volume/frequency, reducing parallel connections, waiting and retrying, and checking server status. Server logs should be analyzed. Sending infrastructure must respect recipient limits. Contacting recipient administrators and verifying DNS configuration may be needed. IP reputation should be considered.
Key findings
- Connection Limits: Exceeding recipient server connection limits triggers the error.
- Temporary Issue: 421 SMTP error indicates a temporary service unavailability.
- Server Overload: Recipient servers may be temporarily overloaded or under maintenance.
- IP Reputation: Sending IP reputation could affect deliverability.
Key considerations
- Throttling: Implement throttling mechanisms and gradually increase sending volume.
- Respect Limits: Configure infrastructure to respect recipient server limits.
- Analyze Logs: Analyze server logs for patterns and underlying issues.
- Contact Admin: If issues persist, contact recipient server administrators.
- Verify DNS: Ensure DNS records are correctly configured.
- Check Settings: Review server settings for connection and rate limits.
What email marketers say
13 marketer opinions
The error 'Server is not currently available, possibly due to too many connections' primarily arises from exceeding connection limits imposed by recipient mail servers, or temporary server issues like overload or maintenance. Solutions involve throttling sending volume and frequency, adjusting parallel connections, waiting and retrying, checking server status, and verifying DNS configurations. Analyzing server logs and potentially contacting recipient server administrators for rate limit adjustments are also recommended. Furthermore, IP reputation should also be considered.
Key opinions
- Connection Limits: Recipient servers have connection limits; exceeding these triggers the error.
- Server Overload: Recipient servers might be temporarily overloaded or undergoing maintenance.
- Throttling: Reducing sending volume, frequency, and parallel connections can alleviate the problem.
- Server Logs: Analyzing server logs helps identify patterns and underlying causes.
- IP Reputation: Considering checking your IP's reputation.
Key considerations
- Adjust Sending: Implement robust throttling mechanisms and gradually increase sending volume.
- Retry Later: Wait for a period before retrying to send emails, allowing the recipient server to recover.
- DNS Configuration: Ensure correct DNS record configuration to avoid deliverability issues.
- Contact Admin: If issues persist, contact the recipient's mail server administrator for assistance or rate limit adjustments.
Marketer view
Email marketer from Email Marketing Forum advises implementing a robust throttling mechanism to avoid overwhelming recipient servers. Gradually increase sending volume and monitor for errors.
23 May 2022 - Email Marketing Forum
Marketer view
Marketer from Email Geeks mentions he has passed the info on to the team to see if there is any more info that can be obtained about the issue(s)
2 Dec 2022 - Email Geeks
What the experts say
1 expert opinions
Exceeding connection limits can cause temporary rejections. Ensure your sending infrastructure respects recipient server limitations and closely monitors sending volume.
Key opinions
- Connection Limits: Exceeding connection limits leads to temporary rejections.
- Sending Infrastructure: Properly configured sending infrastructure is crucial for respecting recipient limits.
- Volume Monitoring: Close monitoring of sending volume is essential.
Key considerations
- Respect Limits: Configure your infrastructure to respect recipient server limitations.
- Monitor Volume: Implement systems to monitor and manage sending volume effectively.
Expert view
Expert from Word to the Wise explains that exceeding connection limits can lead to temporary rejections. She suggests ensuring your sending infrastructure is configured to respect recipient server limitations and to monitor sending volume closely.
20 Apr 2023 - Word to the Wise
What the documentation says
4 technical articles
The 421 SMTP error, 'Service not available, closing transmission channel,' signals a temporary issue. Servers, like Exchange and Postfix, may reject connections to protect resources. Exim utilizes rate limiting to prevent abuse. Resolution involves checking server settings, adjusting throttling policies, and configuring appropriate connection/message rate limits.
Key findings
- Temporary Issue: 421 SMTP error indicates a temporary service unavailability.
- Resource Protection: Servers reject connections to safeguard their resources.
- Rate Limiting: Mail servers employ rate limiting to prevent abuse.
Key considerations
- Check Settings: Review server settings for connection and rate limits.
- Adjust Throttling: Modify throttling policies as needed to optimize performance.
- Configure Limits: Properly configure connection and message rate limits.
Technical article
Documentation from Exim Wiki describes how Exim mail servers use rate limiting to prevent abuse. It suggests configuring appropriate connection and message rate limits.
6 Jul 2024 - Exim
Technical article
Documentation from RFC Editor defines the 421 SMTP error as 'Service not available, closing transmission channel'. It indicates a temporary issue, and the client should try again later. The server might provide additional information.
17 Aug 2023 - RFC Editor
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