IMAP IDLE push does not receive new messages until manual refresh (Fairphone 6 / Android 16)

Checklist

• I have used the search function to see if someone else has already submitted the same bug report.
• I will describe the problem with as much detail as possible.

App

Thunderbird for Android

App version

20.1

Where did you get the app from?

Google Play

Android version

Android 16 (stock Fairphone OS)

Device model

Fairphone Gen. 6

Steps to reproduce

Mail server
All-Inkl (IMAP / Dovecot)

Account type
IMAP

Steps to reproduce

Install Thunderbird.
Configure an IMAP account hosted by All-Inkl.
Enable Push for the INBOX via Manage folders.
Grant the required Alarms & Reminders permission when requested.
Enable background synchronization.
Disable battery optimization for Thunderbird.
Leave Thunderbird running (foreground or background).
Send a test mail to the account from another device/account.

Additional comparison

The same IMAP account was tested on:

• Huawei P30 + Huawei Mail → New messages appear automatically without manual refresh.
• Fairphone 6 + FairEmail → New messages appear automatically without manual refresh.
• Fairphone 6 + Thunderbird → New messages only appear after manual pull-to-refresh.
• The same Wi-Fi network and the same IMAP account were used for all three tests.

The following items have already been verified:

IMAP account (not POP3)
Push enabled for INBOX
Alarms & Reminders permission granted
Background synchronization enabled
Battery optimization disabled
Manual refresh always works

Expected behavior

The new email should appear automatically within a few seconds via IMAP IDLE (Push).

Actual behavior

The message does not appear automatically.
Even when Thunderbird is already open and the INBOX is visible, no new message appears.
The message is only received after manually pulling down to refresh.

Logs

No logs attached yet. I can provide debug logs if needed. I preferred not to upload them initially because they contain personal email addresses and server information.

No source files or tests are named in the report. Start by reproducing the All-Inkl IMAP scenario with debug logging enabled and trace the existing IMAP IDLE push entry point; done means new INBOX messages arrive automatically without manual refresh on the reported Android setup.