Open Bug 2069938 Opened 1 month ago Updated 1 month ago

POP3 messages are deleted from server despite "Leave messages on server" being enabled in Thunderbird 155.0

Categories

(MailNews Core :: Networking: POP, defect)

Product:
MailNews Core
Component:
Networking: POP
Version:
Thunderbird 155
Type:
defect

Tracking

(thunderbird_esr153 unaffected)

Status:
UNCONFIRMED
Tracking Flags:
Tracking Status
thunderbird_esr153 --- unaffected

People

(Reporter: kuzume, Unassigned)

References

Details

(Keywords: regression, regressionwindow-wanted)

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:155.0) Gecko/20100101 Firefox/155.0

Steps to reproduce:

  1. Configure an email account using POP3.
  2. Enable "Leave messages on server" in the POP3 server settings.
  3. Send a new test email to the account and confirm that it exists on the server using webmail.
  4. Start Thunderbird 155.0 and retrieve the new message.
  5. Check the mailbox again using webmail.

Actual results:

After Thunderbird 155.0 retrieved the new message, the message disappeared from the mail server, even though "Leave messages on server" was enabled.

The problem was reproduced on two separate PCs running Thunderbird 155.0.

The same POP3 account worked correctly on two other PCs running Thunderbird 153.2.0esr, where retrieved messages remained on the server.

Expected results:

The retrieved message should have remained on the mail server because the "Leave messages on server" option was enabled.

Summary

POP3 messages are deleted from the server despite "Leave messages on server" being enabled in Thunderbird 155.0.

Description

I found what appears to be a regression in Thunderbird 155.0 related to POP3 accounts.

The affected account is configured to use POP3, and the option "Leave messages on server" is enabled.

However, after Thunderbird 155.0 retrieves newly received messages, the messages disappear from the mail server. This was confirmed by checking the account using webmail.

The problem occurs with newly received messages. For example, I regularly send messages with a Bcc copy to my own address. After Thunderbird 155.0 retrieves those messages, they disappear from the server even though "Leave messages on server" is enabled.

The same account and server work correctly with Thunderbird 153.2.0esr.

Environment

Mail server:

svxxxx.xserver.jp

Account type:

POP3

POP3 settings:

  • Leave messages on server: enabled
  • For at most 30 days: enabled
  • Until I delete or move them from Inbox: enabled

Comparison of affected and unaffected systems

I tested the same mail account on four Windows PCs.

Working correctly

  • Main desktop PC: Thunderbird 153.2.0esr
  • New secondary desktop PC: Thunderbird 153.2.0esr

Messages remain on the server after being retrieved.

Problem occurs

  • Old secondary desktop PC: Thunderbird 155.0
  • Laptop PC: Thunderbird 155.0

Newly received messages are deleted from the server after being retrieved.

Steps to reproduce

  1. Configure a POP3 account.
  2. Enable "Leave messages on server".
  3. Confirm that a newly received message exists on the server using webmail.
  4. Start Thunderbird 155.0.
  5. Retrieve the new message.
  6. Check the server again using webmail.

Actual result

The newly received message disappears from the server after Thunderbird retrieves it.

Expected result

The newly received message should remain on the server because "Leave messages on server" is enabled.

Regression test

On the same PC, changing Thunderbird from version 155.0 to Thunderbird 153.2.0esr caused the problem to disappear.

With Thunderbird 153.2.0esr, the same account retrieves messages while leaving them on the server.

This behavior was reproduced on two separate PCs running Thunderbird 155.0.

status-thunderbird_esr153: --- → unaffected
Component: Untriaged → Networking: POP
Flags: needinfo?(ramona)
Keywords: regression, regressionwindow-wanted
Product: Thunderbird → MailNews Core

Hello!
I tested this issue using Windows 11 version 25H2(OS Build 26200.8457) and did not managed to reproduce this issue.

First I have downloaded TB 155.0 from archive.mozilla.org, using a fresh profile I configured two POP3 accounts using Gmail and Yahoo provider.
For both the Gmail and Yahoo POP3 accounts, I opened the corresponding webmail interface and sent a new test message to each account. I verified that the messages were present on the server before retrieving them with Thunderbird.
I then started Thunderbird 155.0 and retrieved the messages. Messages were downloaded and displayed correctly in Thunderbird.
Afterwards, I returned to the respective webmail interfaces and refreshed the pages. In both cases, the messages were still present on the server.
I also tried different recipient configurations using the POP3 accounts in the To, Cc, Bcc to cover different message delivery scenarios.

After that I tried updating TB from 154.0 to 155.0, using an old profile I performed the same test scenarios. And everything worked as expected, the messages were still displayed on the server.

Afterward I performed the same scenarios on a macOS Sonoma 15.4.7 and the results were the same.

Can you please tell us what email provider were you using when encountering this issue? As with the providers we used didn’t managed to reproduce it.

Flags: needinfo?(ramona)

The issue occurred with a POP3 account hosted by XServer, a Japanese rental/shared hosting provider.

I was able to reproduce the issue with Thunderbird 155.0, while the same account and settings worked correctly with Thunderbird 153.2.0esr.

The POP3 server is svxxxx.xserver.jp.

"svxxxx" is the ID of the shared server I am renting.

Additional information:

I performed some further testing and found that the problem does not occur with every Thunderbird 155.0 installation.

The problem is reproducible with my existing Thunderbird profile, which was migrated from Thunderbird 153.2.0esr to Thunderbird 155.0.

However, I created a new POP3 account on another laptop running Thunderbird 155.0, and the messages were correctly left on the server.

This suggests that the problem may be related to migrated profile data or POP3 state data rather than Thunderbird 155.0 alone.

I also compared the Thunderbird source code between 153.2.0esr and 155.0. The main POP3 client implementation (mailnews/local/src/Pop3Client.sys.mjs) is unchanged between these versions. However, Thunderbird 155.0 includes a significant POP3/mailbox URL refactoring (Bug 2047364).

The existing profile contains a large popstate.dat for the affected POP3 account. I have not yet compared it with the corresponding file after migration to 155.0, because the Thunderbird 153.2.0esr installation is currently working correctly and I do not want to risk disrupting it.

Current test results:

  • Thunderbird 153.2.0esr + existing/migrated profile: works correctly
  • Thunderbird 155.0 + existing/migrated profile: messages are deleted from the server immediately after retrieval
  • Thunderbird 155.0 + newly created POP3 account: works correctly

I will try to compare the POP3 state data between the working 153.2.0esr environment and the problematic 155.0 environment when I can do so safely.

I've been running TB 155.0 (64-bit) since 02-Sept-2026 on two machines, each polling two distinct servers for business or personal emails. Everything seems to be normal -- all relevant emails on both servers are intact. I'm running current Windows 11 on both -- one installed on a new DELL tower at the factory, the other upgraded by the vendor from Windows 10 on a refurb'd LENOVO laptop.

LEAVE MESSAGES ON SERVER is set on both machines, but I also set FOR AT MOST to a time limit, typically 60 or 90 days, and I don't set UNTIL I DELETE THEM. Perhaps one of those is misbehaving in this bug -- and I would suspect UNTIL since it is a binary option.

I'm still not entirely sure what happened to the affected messages.

I confirmed that the messages were present using webmail before downloading them with Thunderbird. However, after receiving the messages with Thunderbird, they did not appear in the Inbox, and they had also disappeared from the server when I checked again using webmail.

What is particularly confusing is that this did not happen to all messages—only some of them disappeared.

For reference, my POP3 settings were as follows:

  • "Leave messages on server" was enabled.
  • "For at most 30 days" was enabled.
  • "Until I delete or move them from Thunderbird" was also enabled.

I am a Japanese speaker and am translating the setting names into English, so the exact wording may be different in the English version of Thunderbird.

One possibility I am wondering about is whether this could be related to migrating my Thunderbird profile from the ESR version to the Release version.

At the moment, I have switched all of my Thunderbird installations back to the ESR version, and everything is working normally.

I also performed another test on a different computer.

I created a new mail account for the same server and tested sending and receiving messages with Thunderbird 155 Release. In that environment, the problem did not occur.

This makes me wonder whether the issue could be related to migrating my profile from the ESR version to the Release version, especially if there have been changes in how Thunderbird manages POP3 mail or related profile data between those versions.

If this is an issue specific to my environment, please feel free to ignore it. I understand that it may not be reproducible or relevant to other users.

Thank you very much for taking the time to investigate this issue and for all your help.

It very well could be you have a filter that catches certain specific messages, with its actions including DELETE MESSAGE FROM SERVER. Those messages would disappear on the server and may not have been downloaded to your computer. This filter does not exist on the second machine so the second one works fine, fetching as it should, putting the message in INBOX, and leaving the original message on the server.

I would suggest going through every single filter line-by-line to see exactly what they do, keeping in mind that the instructions are order-dependent -- you can download and then delete, but you can't delete and then download! And check every account for LEAVE MESSAGES ON SERVER actually being set (checked). Perhaps one or more got unchecked, so the deletes are happening. (Check both machines very carefully, because they might be ever-so-slightly different...)

Reporter, if you do have any filters attached to your POP3 account, please see bug 2068847 comment 9.

See Also: → 2068847

(I would hope this isn't caused by filters.)

Before you try changing any of your filters you ... please download and install https://ftp.mozilla.org/pub/thunderbird/candidates/155.0.1-candidates/build1/win64/en-US/Thunderbird%20Setup%20155.0.1.exe if you are running 155.0 on Windows - it has a fix which has been tested. We would value your immediate feedback that it resolves your problem without introducing new problems.

Flags: needinfo?(kuzume)

Thank you all for your responses.
I work for a company specializing in IT troubleshooting, and I am reaching out to you after having exhausted all other possible solutions.

Although numerous filters are configured, the system operates normally in the "153" state; therefore, it seems unlikely that the filters are the cause of the issue.

Since the problem involves emails disappearing completely—without even remaining in the inbox—I am concerned that applying a patch could lead to further data loss, so I am proceeding with verification very carefully.
In fact, we have already lost some important emails that were expected to arrive.
I appreciate your understanding.

Flags: needinfo?(kuzume)

If any of your filter criteria happened to have empty criteria, bug 2068847 would have caused it to match. Depending on what the filter then did (move, or delete from server) it sounds like it would fit the symptoms. So please check if you had such an empty filter criteria.

Thank you all for your replies.
Upon checking my filters, I found one where the destination folder hadn't been specified.
However, that same filter caused no issues in version 153 ESR.
Could such a small thing really cause version 155 Release to delete emails from the server without actually downloading them?
I have since switched all my email clients to Thunderbird 153 ESR, so it is difficult for me to test version 155 further—I can't risk losing important emails.
It is disappointing to encounter a problem like this, especially since I have been a loyal Thunderbird user since the early days.

See Also: → 2065755

回答ありがとう
ゴミ箱に入っていたら良かったんですが、Thunderbirdのどのメールボックスも存在せず、なおかつサーバからも削除されています
WEBメールの画面を表示して見ていると、Thunderbird でメールを受信した瞬間にある直近一定期間のメールが一瞬で消えてしまいました

Thanks for the reply.
I accidentally sent the message before translating it earlier.
I had hoped it might be in the Trash, but it wasn't in any of my Thunderbird mailboxes, and it had also been deleted from the server.
While I was watching the webmail interface, a batch of recent emails vanished instantly the moment Thunderbird downloaded new mail.

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