Facing a recurring issue with email delivery and could use some guidance to resolve it.
Whenever a campaign is run, a number of email recipients do not receive the email, and the error message received (Delivery failed) is as follows:
Error-details: Syntax error, command unrecognized. The server response
was: 4.3.2 Concurrent connections limit exceeded. Visit
Changes in message store and throttling for concurrent connections - Exchange | Microsoft Learn for more information.
[Hostname=CWLP265MB6150.GBRP265.PROD.OUTLOOK.COM] StackTrace: at
System.Net.Mail.DataStopCommand.CheckResponse(SmtpStatusCode
statusCode, String serverResponse) at
System.Net.Mail.DataStopCommand.Send(SmtpConnection conn) at
System.Net.ClosableStream.Close() at
System.Net.Mail.SmtpClient.Send(MailMessage message) at
NewsletterStudio.Core.Sending.Providers.SmtpEmailServiceProvider.Send(List`1
batch) Source: System
The campaign has over 900+ Recipients and 150 + Delivery failed
As the SMTP Host is: smtp.office365.com
Use SSL = true
and Port = 587
Newsletter studio : V 3.x
Umbraco V8.x
This is a companion discussion topic for the original entry at https://our.umbraco.com/forum/112900-newsletterstudio-delivery-failed-encountering-email-delivery-error-432-concurrent-connections-limit-exceeded