Issue Summary

It has been reported by multiple customers that, after upgrading Jira to 10.3.8 (or any higher version), emails are piling up in the Mail Queue and notification emails take a long time to be sent (at least 5s).

Steps to replicate

The exact steps to replicate are unclear at the moment, since the issue has not been replicated yet in our local environment.

All we know so far is that the impacted customers are on Jira 10.3.8 or any higher version.

Expected behavior

Emails should be sent quickly from the Mail Queue (less than 1s per email)

Observed behavior

• When checking the Mail IDP metrics, we can see that:
  • The Mail Queue size is often high
  • Only 10-12 emails are processed per minute in average
    
• Checking the Jira Outgoing Mail DEBUG logs, we can generally see 5s lost while trying to send the email:

  2025-08-20 18:25:59,375+0000 DEBUG [] Sending mailitem PostprocessingMailQueueItem{delegate=To='admin@localhost' Subject='Updateds for ABC-123: Jira ticket' From='null' FromName='Jira User' Cc='null' Bcc='null' ReplyTo='null' InReplyTo='null' MimeType='text/html' Encoding='UTF-8' Multipart='javax.mail.internet.MimeMultipart@3b9a345d' MessageId='null' ExcludeSubjectPrefix=false'} anonymous    Mail Queue Service [c.atlassian.mail.outgoing] Getting transport for protocol [smtp]
  2025-08-20 18:25:59,375+0000 DEBUG [] Sending mailitem PostprocessingMailQueueItem{delegate=To='admin@localhost' Subject='Updates for ABC-123: Jira ticket' From='null' FromName='Jira User' Cc='null' Bcc='null' ReplyTo='null' InReplyTo='null' MimeType='text/html' Encoding='UTF-8' Multipart='javax.mail.internet.MimeMultipart@3b9a345d' MessageId='null' ExcludeSubjectPrefix=false'} anonymous    Mail Queue Service [c.atlassian.mail.outgoing] Obtaining transport object with cached approach.
  2025-08-20 18:25:59,375+0000 DEBUG [] Sending mailitem PostprocessingMailQueueItem{delegate=To='admin@localhost' Subject='Updates for ABC-123: Jira ticket' From='null' FromName='Jira User' Cc='null' Bcc='null' ReplyTo='null' InReplyTo='null' MimeType='text/html' Encoding='UTF-8' Multipart='javax.mail.internet.MimeMultipart@3b9a345d' MessageId='null' ExcludeSubjectPrefix=false'} anonymous    Mail Queue Service [c.atlassian.mail.outgoing] Got transport: [smtp://jira@mailhost.ea.com]. Connecting
  2025-08-20 18:26:04,452+0000 DEBUG [] Sending mailitem PostprocessingMailQueueItem{delegate=To='admin@localhost' Subject='Updates for ABC-123: Jira ticket' From='null' FromName='Jira User' Cc='null' Bcc='null' ReplyTo='null' InReplyTo='null' MimeType='text/html' Encoding='UTF-8' Multipart='javax.mail.internet.MimeMultipart@3b9a345d' MessageId='null' ExcludeSubjectPrefix=false'} anonymous    Mail Queue Service [c.atlassian.mail.outgoing] Sending message
  2025-08-20 18:26:04,910+0000 DEBUG [] Sending mailitem PostprocessingMailQueueItem{delegate=To='admin@localhost' Subject='Updates for ABC-123: Jira ticket' From='null' FromName='Jira User' Cc='null' Bcc='null' ReplyTo='null' InReplyTo='null' MimeType='text/html' Encoding='UTF-8' Multipart='javax.mail.internet.MimeMultipart@3b9a345d' MessageId='null' ExcludeSubjectPrefix=false'} anonymous    Mail Queue Service [c.atlassian.mail.outgoing] Message was sent with Message-Id <JIRA.20928572.1111111111.11111111.111111111@Atlassian.JIRA>
  

• Checking the Thread Dumps, it seems that Jira is often waiting for a response from the SMTP Mail Server:

  "Sending mailitem PostprocessingMailQueueItem{delegate=To='admin@localhost' Subject='Updates for ABC-123: Jira ticket' From='null' FromName='Jira User' Cc='null' Bcc='null' ReplyTo='null' InReplyTo='null' MimeType='text/html' Encoding='UTF-8' Multipart='javax.mail.internet.MimeMultipart@7312c3b9' MessageId='null' ExcludeSubjectPrefix=false'}" #3506 daemon prio=5 os_prio=0 cpu=61533.35ms elapsed=102774.79s tid=0x00007ef77d0a6110 nid=0xf7b runnable  [0x00007eeacc47f000]
     java.lang.Thread.State: RUNNABLE
  	at sun.nio.ch.Net.poll(java.base@17.0.14/Native Method)
  	at sun.nio.ch.NioSocketImpl.park(java.base@17.0.14/NioSocketImpl.java:186)
  	at sun.nio.ch.NioSocketImpl.timedRead(java.base@17.0.14/NioSocketImpl.java:290)
  	at sun.nio.ch.NioSocketImpl.implRead(java.base@17.0.14/NioSocketImpl.java:314)
  	at sun.nio.ch.NioSocketImpl.read(java.base@17.0.14/NioSocketImpl.java:355)
  	at sun.nio.ch.NioSocketImpl$1.read(java.base@17.0.14/NioSocketImpl.java:808)
  	at java.net.Socket$SocketInputStream.read(java.base@17.0.14/Socket.java:966)
  	at com.sun.mail.util.TraceInputStream.read(TraceInputStream.java:102)
  	at java.io.BufferedInputStream.fill(java.base@17.0.14/BufferedInputStream.java:244)
  	at java.io.BufferedInputStream.read(java.base@17.0.14/BufferedInputStream.java:263)
  	- locked <0x00007f005a002190> (a java.io.BufferedInputStream)
  	at com.sun.mail.util.LineInputStream.readLine(LineInputStream.java:100)
  	at com.sun.mail.smtp.SMTPTransport.readServerResponse(SMTPTransport.java:2456)
  	at com.sun.mail.smtp.SMTPTransport.isConnected(SMTPTransport.java:1440)
  	- locked <0x00007f005a0022f8> (a com.sun.mail.smtp.SMTPTransport)
  	at com.atlassian.mail.server.impl.SMTPMailServerImpl.sendWithMessageId(SMTPMailServerImpl.java:603)
  	at com.atlassian.mail.queue.SingleMailQueueItem.send(SingleMailQueueItem.java:40)
  	at com.atlassian.jira.plugins.inform.batching.PostprocessingMailQueueItem.send(PostprocessingMailQueueItem.java:29)
  	at com.atlassian.jira.mail.CountingMailQueueItemWrapper.send(CountingMailQueueItemWrapper.java:26)
  	at com.atlassian.mail.queue.MailQueueImpl.sendBufferUnderLock(MailQueueImpl.java:83)
  	at com.atlassian.mail.queue.MailQueueImpl.sendBuffer(MailQueueImpl.java:47)
  	at com.atlassian.jira.mail.JiraMailQueue$$Lambda$13502/0x00007efbc35c5990.run(Unknown Source)
  

Notes

This bug is a side effect from the Mail Queue Performance Improvement introduced by https://jira.atlassian.com/browse/JRASERVER-78861 in Jira 10.3.8.

Normally, this improvement introduced in Jira 10.3.8 should help speed up the sending of Jira emails. However, in some cases, it seems to have the opposite effect of slowing down the sending of Jira emails.

Workaround

Disable the "Mail Queue improvement" feature by following the steps below:

• Access the following URL as a Jira administrator account:

  <BASE_URL>/secure/admin/SiteDarkFeatures!default.jspa
  

• Type com.atlassian.jira.smtp.transport.cache.disabled in the Enable dark feature text area and click the Add button