How to fix Hotmail error 451 4.7.652 exceeded maximum number of connections?

Marketer from Email Geeks shares that throttling sending voluntarily and/or expanding the number of IP addresses you send with, so the connections get load balanced / spread, can help fix the connection limits.

Email marketer from SuperUser suggests there could be mail server delays due to various reasons on the receiving end, so it might not always be an immediate issue with the sender and to check mail server status.

Marketer from Email Geeks shares that the SMTP log is saying 'you have to reduce the volume of connections', not 'you need to expand the volume of IPs' and when it says so... It means that you have setup issues or worth, reputation issues! Adding more IPs would only generate is risk of snowshoeing behavior, which is the worst thing to do!

Email marketer from Email Deliverability Blog responds that if using new IPs, warm them up slowly to establish reputation with Microsoft. Start with low volumes and gradually increase.

Email marketer from EmailMarketingForum shares that high engagement rates on your emails can positively influence reputation. Focus on quality content and targeted sending to improve engagement.

Email marketer from SMTPGuru Forums explains that the error means you're opening too many simultaneous connections. Review your email sending script and reduce the number of concurrent threads.

Email Marketer from StackOverflow shares that you need to throttle the number of concurrent SMTP connections to Hotmail/Outlook.com. Space out your emails or use a queueing system.

Email marketer from Webmaster World responds that it could be a reputation issue as Microsoft limits connections from IPs with low reputation. Improve sender reputation by authenticating emails and following best practices.

Email marketer from EmailProviderReviews suggests using connection pools in your application to reuse existing connections instead of creating new ones for each email. This can reduce the number of connection attempts.

Email marketer from Reddit shares that Microsoft has aggressive sending limits. Reduce the number of emails sent per connection and use multiple IPs if volume is high (but manage reputation carefully).

Email marketer from EmailGeeks forums advises monitoring IP and domain reputation using Microsoft's SNDS (Smart Network Data Services) to identify and address any deliverability issues.

Marketer from Email Geeks explains that the number of connections is a function of not just RPM in total, but per IP. Simply the way TCP/IP networking works.

Email marketer from LinuxQuestions.org suggests reviewing your email architecture. Ensure proper DNS records (SPF, DKIM, DMARC) are set up to improve deliverability and reduce connection rejections.

Expert from Spamresource responds that reducing the number of concurrent connections is the primary solution. Ensure your sending infrastructure respects connection limits imposed by receiving mail servers like Hotmail.

Expert from Word to the Wise explains that increasing IPs without addressing the underlying connection issue can lead to snowshoeing, which is detrimental to sender reputation.

Expert from Email Geeks responds that expanding the number of IP addresses is not generally recommended, particularly for a sender that seems to be this naive. It can cause more problems if you don't know what you're doing and seems risky given the circumstances.

Expert from Email Geeks explains that the sender is opening too many SMTP connections to Hotmail and needs to throttle their sending.

Documentation from RFC Editor suggests that SMTP servers may temporarily throttle connections to manage server load. Clients should implement retry mechanisms.

Documentation from Microsoft Docs explains that error 451 4.7.652 indicates the sending IP has exceeded connection limits to Outlook.com/Hotmail. Reduce concurrent connections or spread sending over a longer period.

Documentation from SparkPost explains that 4xx errors are transient failures, and in this case, Hotmail/Outlook.com is temporarily refusing connections due to excessive connection attempts. Implement retry logic with exponential backoff.

Documentation from Postfix.org explains the 'smtpd_client_connection_rate_limit' parameter, used to limit the number of connection attempts from a single IP address per unit time. Reducing this on the sending server may help.