CKB:Maximum number of concurrent server connections has exceeded

Applies To

Cryptshare Version 5.3 and higher

Problem

Some emails cannot be sent and the following error is displayed in the log:

...
ERROR 2022-02-14 11:58:07 MailService - An error occurred when trying to send the download summary email notification.
javax.mail.MessagingException: Got bad greeting from SMTP host: localhost, port: 25, response: 421 4.3.2 The maximum number of concurrent server connections has exceeded a per-source limit, closing transmission channel (localhost)
at com.sun.mail.smtp.SMTPTransport.openServer(SMTPTransport.java:2198)
at com.sun.mail.smtp.SMTPTransport.protocolConnect(SMTPTransport.java:722)
at javax.mail.Service.connect(Service.java:342)
at javax.mail.Service.connect(Service.java:222)
at javax.mail.Service.connect(Service.java:171)
at javax.mail.Transport.send0(Transport.java:230)
at javax.mail.Transport.send(Transport.java:100)
at com.cryptshare.server.core.mail.MailService.sendMessage(MailService.java:501)
at com.cryptshare.server.core.mail.MailService.send(MailService.java:137)
at com.cryptshare.server.core.mail.MailService.send(MailService.java:111)
at com.cryptshare.server.core.mail.MailService.lambda$sendAsync$1(MailService.java:92)
at java.base/java.util.concurrent.FutureTask.run$$$capture(FutureTask.java:264)
at java.base/java.util.concurrent.FutureTask.run(FutureTask.java)
at java.base/java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:304)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
at java.base/java.lang.Thread.run(Thread.java:829)
...

Cause

This problem may occur when the used mail server is configured to allow only a limited number of parallel connections from one IP. In order to increase throughput the Cryptshare server sends some emails in parallel leading to sending more emails than allowed by the mail server.

Solution/Workaround

• Increase your email server's allowed number of parallel connections
• Reduce the number of emails that are sent in parallel by the Cryptshare server. See chapter Advanced Configuration for more details.