I tried later in the day, and the issue is still there. It does seem to be coming from TB 142.0. As I noted, I have seen somewhat slower loading of emails for the last several versions. For example, I would delete an email. While the email did disappear from the list right away, and the previous email opened, I saw the lower right bar from the activity manager activated for a minute or so. I also noticed that, if I try to compact files while the lower right bar shows activity, the compact process takes much longer. Even with 142.0, the process does eventually work as it should.

Since I really cannot work with this, I restored to TB 141.0. It gave me a error that I was using an older version on my profile. Just to be safe, I restored the profile as it was on 8/20 before I made the upgrade to 142.0. After the restore, I am back to the performance I had before. I am sorry I could not provide more information as I am only a moderate skill when it comes to software, and I was not sure what else to look for or try.

Help. I started having the same issue with TB 141.0 today, even though it had been working fine. This time I am getting authentication errors with imap.google.com. Of course, it has been working fine. No changes were made since I turned of the computer last evening. I tried reinstalling TB 141.0. That made no difference.

This is disparate. Every time it tries to load a message it takes forever, apparently because of the authentication issues. This make TB usable.

I thought this might be a Bitdefender issue, since Bitdefender apparently made a major update this morning. However, I have listed the thunderbird.exe folder as an exception in Bitdefender -- and that does not seem to have helped. I did file a case with Bitdefender, and I am waiting for a response.

I have now confirmed that this is mostly a Bitdefender issue. Listing Thunderbird.exe as exceptions, suggested by the Bitdefender team, did not make any difference. Bitdefender does not have a way to pause all activity, like my old Kaspersky did. However, after turning on and off various settings, I found that changing the last setting under Online Threat Prevention to "Don't Scan Emails" seems to have corrected the issue. I still see a few slow responses from time to time, but that might be Google.

Having said that, it seems to me that the protocols used within Thunderbird to access IMAP email and various other activities seems to have changed in the later versions of TB, past around 128. I just seem to see a lot more activity, including authentications, when I do things as simple as delete one email and go to the next. Perhaps these actions by TB are necessary to insure proper syncing, but I just wonder if there might be less verbose methods that would be faster and perhaps also less prone to trigger reactions from things outside Thunderbird like AV.

I still have a case open with Bitdefender to address the slowing email issues.

I still have a case open with Bitdefender to address the slowing email issues.

Sorted out I hope?

Yes. I found that setting Bitdefender to not scan emails was an effective workaround. Shortly thereafter, Bitdefender stopped causing issues even when set to scan emails. I still seem to see a lot more interaction taking place to keep up with IMAP than I used to see on older versions of Thunderbird. It causes delays of a minute or so from time to time, but nothing like I was experiencing before with Bitdefender. I think Bitdefender was just slowing down all those different communications.

I am not using bitdefender but have this same problem - all email folder sync, compose, and send are super slow with my UW Google account.

My system is windows server 2025 and it is running Crowdstrike EDR on it. What logs should I look at?

Thunderbird is unusable

 Application Basics

   Name: Thunderbird
   Version: 145.0
   Build ID: 20251112194829
   Distribution ID:

   Update Channel: release
   User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:145.0) Gecko/20100101 Thunderbird/145.0
   OS: Windows_NT 10.0 26100
   OS Theme:

   Launcher Process: Enabled
   Multiprocess Windows: 0/0
   Fission Windows: 0/0
             Enabled by default
   Remote Processes: 1
   Enterprise Policies: Inactive
   Google Location Service Key: Missing
   Google Safebrowsing Key: Missing
   Mozilla Location Service Key: Missing
   Safe Mode: false
   Memory Size (RAM): 256 GB
   Disk Space Available: 3,139 GB

 Mail and News Accounts
   account1:
     INCOMING: account1, , (imap) imap.gmail.com:993, SSL, OAuth2
     OUTGOING: , smtp.uw.edu:465, SSL, passwordCleartext, true

   account2:
     INCOMING: account2, , (none) Local Folders, plain, passwordCleartext

   account4:
     INCOMING: account4, , (imap) imap.fastmail.com:993, SSL, passwordCleartext
     OUTGOING: , smtp.fastmail.com:587, alwaysSTARTTLS, passwordCleartext, true

   account5:
     INCOMING: account5, , (imap) outlook.office365.com:993, SSL, OAuth2
     OUTGOING: , smtp.uw.edu:465, SSL, passwordCleartext, true

   account6:
     INCOMING: account6, , (imap) outlook.office365.com:993, SSL, OAuth2
     OUTGOING: , smtp.uw.edu:465, SSL, passwordCleartext, true

   account8:
     INCOMING: account8, , (imap) outlook.office365.com:993, SSL, OAuth2
     OUTGOING: , smtp.uw.edu:465, SSL, passwordCleartext, true

   account9:
     INCOMING: account9, , (imap) outlook.office365.com:993, SSL, OAuth2
     OUTGOING: , smtp.uw.edu:465, SSL, passwordCleartext, true

   account10:
     INCOMING: account10, , (imap) outlook.office365.com:993, SSL, OAuth2
     OUTGOING: , smtp.uw.edu:465, SSL, passwordCleartext, true

 Libraries

     Library
     Status
     Expected minimum version
     Version in use
     Path

       RNP (OpenPGP)
       OK
       0.17.1
       0.17.1.MZLA.145.0.botan
       C:\Program Files\Mozilla Thunderbird\rnp.dll

       OTR
       Failed to load. OTR chat encryption will not work.
       -
       -
       -

 Calendar Settings

     mbw@uw.edu

       Name
       Value

       Name:
       Type: gdata
       Disabled: true
       Username:
       URI:
       Refresh Interval: 30
       Read-only: false
       Suppress Alarms: true
       Cache Enabled:
       iMIP Identity: id1
       iMIP Disabled:
       iMIP Account:
       Organizer Id:
       Force Email Scheduling:
       Popup Alarms Supported:
       Alarms on Invitation Supported:
       Max Alarms Per Event:
       Attachment Supported:
       Max Categories:
       Privacy State Supported:
       Priority Supported:
       Event Supported:
       Task Supported:
       Local Time Supported:
       UTC/GMT Supported:
       Auto-Scheduling Supported:

     matt.and.chiaki@gmail.com

       Name
       Value

       Name:
       Type: gdata
       Disabled: true
       Username:
       URI:
       Refresh Interval: 60
       Read-only: false
       Suppress Alarms: false
       Cache Enabled:
       iMIP Identity: id3
       iMIP Disabled:
       iMIP Account:
       Organizer Id:
       Force Email Scheduling:
       Popup Alarms Supported:
       Alarms on Invitation Supported:
       Max Alarms Per Event:
       Attachment Supported:
       Max Categories:
       Privacy State Supported:
       Priority Supported:
       Event Supported:
       Task Supported:
       Local Time Supported:
       UTC/GMT Supported:
       Auto-Scheduling Supported:

 Crash Reports for the Last 3 Days

 Remote Processes

   Type: Count

   GPU: 1

 Add-ons

     Name
     Type
     Version
     Enabled
     Location
     ID

       Amazon.com
       extension
       1.1
       true
       app-builtin
       amazondotcom@search.mozilla.org

       Bing
       extension
       1.0
       true
       app-builtin
       bing@search.mozilla.org

       DuckDuckGo
       extension
       1.0
       true
       app-builtin
       ddg@search.mozilla.org

       Google
       extension
       1.0
       true
       app-builtin
       google@search.mozilla.org

       Wikipedia (en)
       extension
       1.0
       true
       app-builtin
       wikipedia@search.mozilla.org

       System theme — auto
       theme
       1.4.2
       true
       app-builtin
       default-theme@mozilla.org

       Provider for Google Calendar
       extension
       128.5.7
       false
       app-profile
       {a62ef8ec-5fdc-40c2-873c-223b8a6925cc}

       Dark
       theme
       1.3.1
       false
       app-builtin
       thunderbird-compact-dark@mozilla.org

       Light
       theme
       1.3.1
       false
       app-builtin
       thunderbird-compact-light@mozilla.org

 Security Software

   Type: Name

     Antivirus:
     Antispyware:
     Firewall:

 Legacy User Stylesheets

   Active: false
   Stylesheets: No stylesheets found

As noted on the other thread -

slow performance occurs exclusively with my Gmail inbox - I have multiple mailboxs in "the bird" and my pobox email work as expected while gmail is very slow

In my case, Bitdefender was interfering when Thunderbird tried to authenticate to Google. Apparently, this authentication happens very frequently, much more often than I would have thought. Perhaps there is something else on your system that has the same effect? Other than that, I don't know enough to really provide any helpful advice.