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Thunderbird 153 ESR freezes during POP3 mail retrieval and while idle on Windows 10

Thunderbird App crash
kawamtmy replied 1 hour ago
kawamtmy
kawamtmy

Hello, I am experiencing repeated freezes in Thunderbird 153 ESR on Windows 10. I have been investigating this problem since mid-October 2026, but have not been able to identify the cause. Thunderbird is essential for my daily work, so I would appreciate advice on identifying the cause and restoring stable operation.

1. System environment - PC: dynabook R63/B - OS: Windows 10, 64-bit - Thunderbird: 153.6.0esr, 64-bit - Mail provider: @nifty (Japan) - Incoming mail: POP3 over SSL/TLS, port 995 - Security software: Super Security (Japanese security software) - Mail storage: Local mbox files

2. When the problem started Thunderbird worked reasonably well until September 2026. The freezing problem began around mid-October 2026. Windows Reliability Monitor recorded Thunderbird as "Stopped responding" on October 19, 2026, at 9:48 a.m. This is the earliest recorded incident I have found, although the problem may have started earlier. Thunderbird update history: - September 18: 153.3.1esr - October 1: 153.4.0esr - October 14: 153.5.0esr - October 21: 153.5.1esr - October 28: 153.6.0esr The first recorded freeze occurred after the update to 153.5.0esr. However, I have not established that the update caused the problem.

3. Symptoms Thunderbird becomes unresponsive and usually has to be forcibly terminated. During these freezes, Windows Task Manager often shows Thunderbird using approximately 30–40% CPU, repeatedly around 39–40%. Freezes also occur when Thunderbird is using only about 1.1 GB of memory. On other occasions, memory usage has increased to approximately 2.56 GB. The problem occurs under several different conditions: 1. During manual POP3 mail retrieval. 2. After repeated manual mail retrieval operations. 3. Approximately 30 minutes after a single mail retrieval, even when Thunderbird is left idle. 4. Sometimes after replying to messages or copying messages to other folders. 5. In both normal mode and Troubleshoot Mode. 6. Sometimes during the first mail retrieval after starting Thunderbird. Other Windows applications generally remain responsive when Thunderbird freezes. Restarting Windows sometimes restores normal Thunderbird operation temporarily, but the problem returns.

4. Troubleshooting already performed I have already tried the following: - Reinstalled Thunderbird from the official website. - Created a new Thunderbird test profile. - Disabled extensions. - Disabled hardware acceleration. - Disabled global search and indexing. - Removed all active Thunderbird message filters for testing. - Disabled the anti-spam component of Super Security. - Disabled automatic mail checking and automatic downloading. - Tested manual mail retrieval in Troubleshoot Mode. - Reduced the size of the Inbox from approximately 4.1 GB to 2.4 GB. - Performed a full antivirus scan, which detected no threats. The new profile initially worked, including several successful POP3 retrievals, but the freezing problem later returned. Reinstalling Thunderbird did not resolve the issue. The anti-spam component remains disabled for testing, but the problem continues.

5. Windows error records Windows Reliability Monitor recorded Thunderbird as unresponsive on October 19, 2026, at 9:48 a.m. Windows Event Viewer also recorded an Application Hang, Event ID 1002, on October 30, 2026, at approximately 4:23 a.m. The affected executable was thunderbird.exe, version 153.6.0.0. These records confirm the application hang but do not identify its underlying cause.

6. POP3 communication Earlier POP3 logging confirmed that Thunderbird connected to the @nifty POP3 server and received a CAPA response. However, I have not identified which POP3 or internal Thunderbird operation was active at the exact moment of the freeze. I have not collected a process memory dump.

7. Potentially related Mozilla bug reports I found two reports that may be relevant: - Bug 2080699: POP mail retrieval becomes unresponsive in Thunderbird 153.4.0esr. - Bug 2031744: Freezing potentially related to mail index (.msf) files and background processing. Some symptoms are similar, but I cannot determine whether they have the same underlying cause.

8. Questions I would appreciate advice on the following: 1. Are there known POP3-related freezes or high-CPU problems in Thunderbird 153 ESR, particularly after the October 2026 updates? 2. Could background mail processing, folder maintenance, or mail index files explain a freeze that occurs while Thunderbird is idle? 3. Could interaction with antivirus software or Windows networking components cause these symptoms? 4. Are there diagnostic steps that can help identify the cause without repeatedly freezing Thunderbird or risking existing mail data? 5. Would this information be more appropriate as an additional comment on an existing Bugzilla report or as a separate bug report? I have already spent considerable time testing different configurations. I would prefer to avoid repeating tests that have not helped. I have a backup of my Thunderbird profile and would like to preserve my existing mail data.

Thank you for your assistance.

Hello, I am experiencing repeated freezes in Thunderbird 153 ESR on Windows 10. I have been investigating this problem since mid-October 2026, but have not been able to identify the cause. Thunderbird is essential for my daily work, so I would appreciate advice on identifying the cause and restoring stable operation. 1. System environment - PC: dynabook R63/B - OS: Windows 10, 64-bit - Thunderbird: 153.6.0esr, 64-bit - Mail provider: @nifty (Japan) - Incoming mail: POP3 over SSL/TLS, port 995 - Security software: Super Security (Japanese security software) - Mail storage: Local mbox files 2. When the problem started Thunderbird worked reasonably well until September 2026. The freezing problem began around mid-October 2026. Windows Reliability Monitor recorded Thunderbird as "Stopped responding" on October 19, 2026, at 9:48 a.m. This is the earliest recorded incident I have found, although the problem may have started earlier. Thunderbird update history: - September 18: 153.3.1esr - October 1: 153.4.0esr - October 14: 153.5.0esr - October 21: 153.5.1esr - October 28: 153.6.0esr The first recorded freeze occurred after the update to 153.5.0esr. However, I have not established that the update caused the problem. 3. Symptoms Thunderbird becomes unresponsive and usually has to be forcibly terminated. During these freezes, Windows Task Manager often shows Thunderbird using approximately 30–40% CPU, repeatedly around 39–40%. Freezes also occur when Thunderbird is using only about 1.1 GB of memory. On other occasions, memory usage has increased to approximately 2.56 GB. The problem occurs under several different conditions: 1. During manual POP3 mail retrieval. 2. After repeated manual mail retrieval operations. 3. Approximately 30 minutes after a single mail retrieval, even when Thunderbird is left idle. 4. Sometimes after replying to messages or copying messages to other folders. 5. In both normal mode and Troubleshoot Mode. 6. Sometimes during the first mail retrieval after starting Thunderbird. Other Windows applications generally remain responsive when Thunderbird freezes. Restarting Windows sometimes restores normal Thunderbird operation temporarily, but the problem returns. 4. Troubleshooting already performed I have already tried the following: - Reinstalled Thunderbird from the official website. - Created a new Thunderbird test profile. - Disabled extensions. - Disabled hardware acceleration. - Disabled global search and indexing. - Removed all active Thunderbird message filters for testing. - Disabled the anti-spam component of Super Security. - Disabled automatic mail checking and automatic downloading. - Tested manual mail retrieval in Troubleshoot Mode. - Reduced the size of the Inbox from approximately 4.1 GB to 2.4 GB. - Performed a full antivirus scan, which detected no threats. The new profile initially worked, including several successful POP3 retrievals, but the freezing problem later returned. Reinstalling Thunderbird did not resolve the issue. The anti-spam component remains disabled for testing, but the problem continues. 5. Windows error records Windows Reliability Monitor recorded Thunderbird as unresponsive on October 19, 2026, at 9:48 a.m. Windows Event Viewer also recorded an Application Hang, Event ID 1002, on October 30, 2026, at approximately 4:23 a.m. The affected executable was thunderbird.exe, version 153.6.0.0. These records confirm the application hang but do not identify its underlying cause. 6. POP3 communication Earlier POP3 logging confirmed that Thunderbird connected to the @nifty POP3 server and received a CAPA response. However, I have not identified which POP3 or internal Thunderbird operation was active at the exact moment of the freeze. I have not collected a process memory dump. 7. Potentially related Mozilla bug reports I found two reports that may be relevant: - Bug 2080699: POP mail retrieval becomes unresponsive in Thunderbird 153.4.0esr. - Bug 2031744: Freezing potentially related to mail index (.msf) files and background processing. Some symptoms are similar, but I cannot determine whether they have the same underlying cause. 8. Questions I would appreciate advice on the following: 1. Are there known POP3-related freezes or high-CPU problems in Thunderbird 153 ESR, particularly after the October 2026 updates? 2. Could background mail processing, folder maintenance, or mail index files explain a freeze that occurs while Thunderbird is idle? 3. Could interaction with antivirus software or Windows networking components cause these symptoms? 4. Are there diagnostic steps that can help identify the cause without repeatedly freezing Thunderbird or risking existing mail data? 5. Would this information be more appropriate as an additional comment on an existing Bugzilla report or as a separate bug report? I have already spent considerable time testing different configurations. I would prefer to avoid repeating tests that have not helped. I have a backup of my Thunderbird profile and would like to preserve my existing mail data. Thank you for your assistance.

All Replies (1)

kawamtmy
kawamtmy Question owner

Additional findings from November 9–10, 2026

Hello,

I would like to provide an update on my Thunderbird freezing issue.

I performed further tests on November 9–10, 2026, and obtained the following results.

1. Freezing after restarting Windows

- I restarted Windows 10. - I started Thunderbird 153.6.0esr in Troubleshoot Mode. - I manually checked for new POP3 messages from @nifty. - All messages were successfully received, although the process took longer than usual. - Approximately 30 minutes later, Thunderbird froze without further user interaction. - Thunderbird's CPU usage was approximately 40%. - I had to terminate Thunderbird using Windows Task Manager.

2. Freezing triggered by manual mail retrieval

I performed another test under different conditions.

- I started Thunderbird in Troubleshoot Mode. - I left Thunderbird running for 60 minutes without manually checking for new messages. - Thunderbird remained responsive throughout those 60 minutes. - I then manually checked for new POP3 messages. - Thunderbird froze during the retrieval process. - CPU usage again remained at approximately 40%. - I had to terminate Thunderbird using Task Manager.

Both automatic checks for new messages at startup and periodic automatic checks are disabled.

3. Windows Event Viewer findings

Windows Event Viewer recorded the following information for a freeze on November 9:

- Application Hang — Event ID 1002 - Windows Error Reporting — Event ID 1001 - Event name: AppHangB1 - Application: thunderbird.exe - Version: 153.6.0.0 - Hang type: Top level window is idle - Failure bucket ID: 1522252194653677288

The Windows Error Reporting record also lists diagnostic files named `minidump.mdmp` and `memory.hdmp`. I have not verified whether these files are still available.

4. Mail provider verification

I confirmed that @nifty webmail can receive and send messages normally.

5. Request for advice

These results suggest that the freezing may be associated with POP3 mail retrieval or processing triggered by retrieval, although the cause remains unknown.

Could you advise me on how to identify the cause, particularly whether there are Thunderbird diagnostic logs or other safe debugging methods that would help?

My goal is to keep Thunderbird running continuously and automatically check for new mail every 10 minutes.

I would like to avoid repeating tests already performed and preserve my existing email data.

Thank you for your assistance.

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