And this is when the notification gets delivered:
10-15 15:38:57.686 14361 14389 V ImapBackendPusher: Refreshing ImapBackendPusher (at least one retry timer has expired)
10-15 15:38:57.690 14361 14389 V ImapBackendPusher: ImapBackendPusher.updateFolders(): [INBOX]
10-15 15:38:57.695 14361 14389 V ImapFolderPusher: Starting ImapFolderPusher for Morfik / INBOX
10-15 15:38:57.697 14361 8904 V ImapFolderPusher$start: Starting ImapFolderPusher thread for Morfik / INBOX
10-15 15:38:57.700 14361 8904 V AndroidPowerManager$AndroidWakeLock: AndroidWakeLock for tag ImapFolderPusher-Morfik-INBOX / id 8: Create
10-15 15:38:57.704 14361 8904 V AndroidPowerManager$AndroidWakeLock: AndroidWakeLock for tag ImapFolderPusher-Morfik-INBOX / id 8: acquired with no timeout.
10-15 15:38:57.711 14361 14384 I MessagingController: Running command 'synchronizeMailbox', seq = 56 (background priority)
10-15 15:38:57.722 14361 14384 D MessagingController: Last folder list refresh @ Fri Oct 15 15:17:34 GMT+02:00 2021. Not refreshing now.
10-15 15:38:57.732 14361 14384 I ImapSync: Synchronizing folder Morfik:INBOX
10-15 15:38:57.732 14361 14384 V ImapSync: SYNC: About to get local folder INBOX
10-15 15:38:57.738 14361 14384 V ImapSync: SYNC: About to get remote folder INBOX
10-15 15:38:57.738 14361 14384 V ImapSync: SYNC: About to open remote folder INBOX
10-15 15:38:57.741 14361 14384 V RealImapConnection: conn264785677>>> 5 NOOP
10-15 15:38:58.179 14361 14384 V ImapResponseParser: conn264785677<<<#5# [OK, Success]
10-15 15:38:58.181 14361 14384 V RealImapConnection: conn264785677>>> 6 EXAMINE "INBOX"
10-15 15:38:58.355 14361 14384 V ImapResponseParser: conn264785677<<<#null# [FLAGS, [\Answered, \Flagged, \Draft, \Deleted, \Seen, $NotPhishing, $Phishing]]
10-15 15:38:58.356 14361 14384 V ImapResponseParser: conn264785677<<<#null# [OK, [PERMANENTFLAGS, []], Flags permitted.]
10-15 15:38:58.357 14361 14384 V ImapResponseParser: conn264785677<<<#null# [OK, [UIDVALIDITY, 1], UIDs valid.]
10-15 15:38:58.359 14361 14384 V ImapResponseParser: conn264785677<<<#null# [2, EXISTS]
10-15 15:38:58.360 14361 14384 V ImapResponseParser: conn264785677<<<#null# [0, RECENT]
10-15 15:38:58.361 14361 14384 V ImapResponseParser: conn264785677<<<#null# [OK, [UIDNEXT, 757], Predicted next UID.]
10-15 15:38:58.362 14361 14384 V ImapResponseParser: conn264785677<<<#null# [OK, [HIGHESTMODSEQ, 228249]]
10-15 15:38:58.363 14361 14384 V ImapResponseParser: conn264785677<<<#6# [OK, [READ-ONLY], INBOX selected. (Success)]
10-15 15:38:58.364 14361 14384 D RealImapFolder: Got untagged EXISTS with value 2 for Morfik:INBOX/MessagingController/conn264785677
10-15 15:38:58.365 14361 14384 D RealImapFolder: Got UidNext = 757 for Morfik:INBOX/MessagingController/conn264785677
10-15 15:38:58.372 14361 14384 V ImapSync: SYNC: Remote message count for folder INBOX is 2
10-15 15:38:58.372 14361 14384 V ImapSync: SYNC: About to get messages 1 through 2 for folder INBOX
10-15 15:38:58.375 14361 14384 V RealImapConnection: conn264785677>>> 7 UID SEARCH 1:2 SINCE 15-Apr-2021 NOT DELETED
10-15 15:38:58.640 14361 14384 V ImapResponseParser: conn264785677<<<#null# [SEARCH, 755, 756]
10-15 15:38:58.641 14361 14384 V ImapResponseParser: conn264785677<<<#7# [OK, SEARCH completed (Success)]
10-15 15:38:58.645 14361 14384 V ImapSync: SYNC: Got 2 messages for folder INBOX
10-15 15:38:58.648 14361 14384 V ImapSync: Message with uid 756 has not yet been downloaded
10-15 15:38:58.652 14361 14384 V ImapSync: Message with uid 755 is present in the local store
10-15 15:38:58.654 14361 14384 D ImapSync: SYNC: Have 1 unsynced messages
10-15 15:38:58.658 14361 14384 D ImapSync: SYNC: About to fetch 1 unsynced messages for folder INBOX
10-15 15:38:58.661 14361 14384 V RealImapConnection: conn264785677>>> 8 UID FETCH 756 (UID FLAGS INTERNALDATE RFC822.SIZE BODY.PEEK[HEADER.FIELDS (date subject from content-type to cc reply-to message-id references in-reply-to X-K9mail-Identity Chat-Version)])
10-15 15:38:58.856 14361 14384 V RealImapConnection: conn264785677<<<#null# [2, FETCH, [UID, 756, RFC822.SIZE, 5139, INTERNALDATE, 15-Oct-2021 13:25:48 +0000, FLAGS, [], BODY, [HEADER.FIELDS, [date, subject, from, content-type, to, cc, reply-to, message-id, references, in-reply-to, X-K9mail-Identity, Chat-Version]], To: Morfik <mail-sent-to@gmail.com>
10-15 15:38:58.856 14361 14384 V RealImapConnection: From: Mikhail Morfikov <mail-sent-from@gmail.com>
10-15 15:38:58.856 14361 14384 V RealImapConnection: Subject: test
10-15 15:38:58.856 14361 14384 V RealImapConnection: Message-ID: <a1439ea2-7118-ff8a-709c-c0f08649dd79@gmail.com>
10-15 15:38:58.856 14361 14384 V RealImapConnection: Date: Fri, 15 Oct 2021 15:25:47 +0200
10-15 15:38:58.856 14361 14384 V RealImapConnection: Content-Type: text/plain; charset=utf-8
10-15 15:38:58.856 14361 14384 V RealImapConnection:
10-15 15:38:58.856 14361 14384 V RealImapConnection: ]]
10-15 15:38:58.867 14361 14384 V RealImapConnection: conn264785677<<<#8# [OK, Success]
10-15 15:38:58.868 14361 14384 D ImapSync: SYNC: Synced unsynced messages for folder INBOX
10-15 15:38:58.869 14361 14384 D ImapSync: SYNC: Have 0 large messages and 1 small messages out of 1 unsynced messages
10-15 15:38:58.870 14361 14384 D ImapSync: SYNC: Fetching 1 small messages for folder INBOX
10-15 15:38:58.872 14361 14384 V RealImapConnection: conn264785677>>> 9 UID FETCH 756 (UID BODY.PEEK[])
10-15 15:38:59.475 14361 14384 V RealImapConnection: conn264785677<<<#null# [2, FETCH, [UID, 756, BODY, [], 1]]
10-15 15:38:59.509 14361 14384 D BinaryTempFileBody$BinaryTempFileBodyInputStream: Deleting temporary binary file: body4899007371212010983.tmp
10-15 15:38:59.532 14361 14384 V LockableDatabase: LockableDatabase: Transaction ended, took 4 ms / com.fsck.k9.storage.messages.SaveMessageOperations.saveMessage(SaveMessageOperations.kt:81)
10-15 15:38:59.535 14361 14384 V ImapSync$downloadSmallMessages: About to notify listeners that we got a new small message Morfik:INBOX:756
10-15 15:38:59.548 14361 14384 V MessagingController$ControllerSyncListener: Creating notification for message INBOX:756
10-15 15:38:59.591 14361 14384 V RealImapConnection: conn264785677<<<#9# [OK, Success]
10-15 15:38:59.592 14361 14384 D ImapSync: SYNC: Done fetching small messages for folder INBOX
10-15 15:38:59.593 14361 14384 D ImapSync: SYNC: Fetching large messages for folder INBOX
10-15 15:38:59.593 14361 14384 D ImapSync: SYNC: Done fetching large messages for folder INBOX
10-15 15:38:59.594 14361 14384 D ImapSync: SYNC: About to sync flags for 1 remote messages for folder INBOX
10-15 15:38:59.596 14361 14384 V RealImapConnection: conn264785677>>> 10 UID FETCH 755 (UID FLAGS)
10-15 15:39:00.097 14361 14384 V RealImapConnection: conn264785677<<<#null# [1, FETCH, [UID, 755, FLAGS, [\Seen]]]
10-15 15:39:00.098 14361 14384 V RealImapConnection: conn264785677<<<#10# [OK, Success]
10-15 15:39:00.102 14361 14384 D ImapSync: SYNC: Synced remote messages for folder INBOX, 1 new messages
10-15 15:39:00.115 14361 14384 D ImapSync: Done synchronizing folder Morfik:INBOX @ Fri Oct 15 15:39:00 GMT+02:00 2021 with 1 new messages
10-15 15:39:00.117 14361 14384 I ImapSync: Done synchronizing folder Morfik:INBOX
10-15 15:39:00.118 14361 14384 I MessagingController: Command 'synchronizeMailbox' completed
10-15 15:39:00.119 14361 8904 V RealImapFolderIdler: ImapFolderIdler[INBOX].idle()
10-15 15:39:00.121 14361 8904 V RealImapConnection: conn264785677>>> 11 NOOP
10-15 15:39:00.227 14361 8904 V ImapResponseParser: conn264785677<<<#11# [OK, Success]
10-15 15:39:00.229 14361 8904 V RealImapConnection: conn264785677>>> 12 EXAMINE "INBOX"
10-15 15:39:00.795 14361 8904 V ImapResponseParser: conn264785677<<<#null# [FLAGS, [\Answered, \Flagged, \Draft, \Deleted, \Seen, $NotPhishing, $Phishing]]
10-15 15:39:00.796 14361 8904 V ImapResponseParser: conn264785677<<<#null# [OK, [PERMANENTFLAGS, []], Flags permitted.]
10-15 15:39:00.797 14361 8904 V ImapResponseParser: conn264785677<<<#null# [OK, [UIDVALIDITY, 1], UIDs valid.]
10-15 15:39:00.799 14361 8904 V ImapResponseParser: conn264785677<<<#null# [2, EXISTS]
10-15 15:39:00.807 14361 8904 V ImapResponseParser: conn264785677<<<#null# [0, RECENT]
10-15 15:39:00.808 14361 8904 V ImapResponseParser: conn264785677<<<#null# [OK, [UIDNEXT, 757], Predicted next UID.]
10-15 15:39:00.813 14361 8904 V ImapResponseParser: conn264785677<<<#null# [OK, [HIGHESTMODSEQ, 228249]]
10-15 15:39:00.814 14361 8904 V ImapResponseParser: conn264785677<<<#12# [OK, [READ-ONLY], INBOX selected. (Success)]
10-15 15:39:00.819 14361 8904 D RealImapFolder: Got untagged EXISTS with value 2 for Morfik:INBOX/ImapFolderPusher-Morfik-INBOX/conn264785677
10-15 15:39:00.819 14361 8904 D RealImapFolder: Got UidNext = 757 for Morfik:INBOX/ImapFolderPusher-Morfik-INBOX/conn264785677
10-15 15:39:00.822 14361 8904 V RealImapConnection: Connection conn264785677 has 21 capabilities
10-15 15:39:00.824 14361 8904 V RealImapConnection: conn264785677>>> 13 IDLE
10-15 15:39:01.017 14361 8904 V RealImapConnection: conn264785677<<<#+# [idling]
10-15 15:39:01.021 14361 8904 V AndroidPowerManager$AndroidWakeLock: AndroidWakeLock for tag ImapFolderPusher-Morfik-INBOX / id 8: releasing after 3316 ms, timeout = null ms