Is there some secret config sauce I'm unaware of to get IMAP push notifications working with Outlook ?

My present situation is that non-Outlook users (e.g. Apple iOS, Apple Mail etc.) work perfectly with the config below. New emails get pushed, deletes get reflected, all is happy in the world.

But with Outlook nothing. You send a user an email, nothing happens in their inbox until you manually refresh by checking for new mails or waiting for the auto-check to kick in (sometimes switching between IMAP folders also does the trick).

I know Outlook has a long history of being a mess when it comes to standards compliance, but surely it can't be this bad ?

doveconf -n :

# 2.3.18 (9dd8408c18): /etc/dovecot/dovecot.conf # Pigeonhole version 0.5.18 (0bc28b32) # OS: Linux 5.10.0-11-amd64 x86_64 Debian 11.2 xfs # Hostname: foobar.example.com auth_verbose = yes auth_verbose_passwords = sha1:7 doveadm_password = # hidden, use -P to show it imap_capability = +SPECIAL-USE imapc_features = rfc822.size fetch-headers fetch-bodystructure imapc_port = 993 imapc_ssl = imaps mail_location = maildir:/foo_data/mail/%d/%n/Maildir mail_plugins = notify replication push_notification managesieve_notify_capability = mailto managesieve_sieve_capability = fileinto reject envelope encoded-character vacation subaddress comparator-i;ascii-numeric relational regex imap4flags copy include variables body enotify environment mailbox date index ihave duplicate mime foreverypart extracttext imapsieve vnd.dovecot.imapsieve namespace inbox { inbox = yes location = mailbox "Deleted Messages" { auto = no special_use = \Trash } mailbox Drafts { special_use = \Drafts } mailbox Junk { auto = subscribe special_use = \Junk } mailbox Sent { special_use = \Sent } mailbox "Sent Messages" { special_use = \Sent } mailbox Trash { special_use = \Trash } prefix = } passdb { args = /etc/dovecot/local_sql_users.conf driver = sql } plugin { imapsieve_mailbox1_before = file:/etc/dovecot/imap_sieve/spam.sieve imapsieve_mailbox1_causes = COPY imapsieve_mailbox1_name = Junk imapsieve_mailbox2_before = file:/etc/dovecot/imap_sieve/ham.sieve imapsieve_mailbox2_causes = COPY imapsieve_mailbox2_from = Junk imapsieve_mailbox2_name = * sieve = file:~/sieve;active=~/.dovecot.sieve sieve_global_extensions = +vnd.dovecot.pipe +vnd.dovecot.environment sieve_pipe_bin_dir = /etc/dovecot/imap_sieve sieve_plugins = sieve_imapsieve sieve_extprograms } protocols = imap lmtp sieve service auth { unix_listener /var/spool/postfix/private/dovecot-auth { group = postfix mode = 0660 user = postfix } vsz_limit = 2 G } service doveadm { inet_listener { port = 11867 ssl = yes } } service imap-login { process_min_avail = 5 service_count = 1 } service lmtp { process_min_avail = 5 unix_listener /var/spool/postfix/private/dovecot-lmtp { group = postfix mode = 0660 user = postfix } user = foo_virtmail } service managesieve-login { inet_listener sieve { port = 4190 } inet_listener sieves { address = port = 5190 ssl = yes } } ssl = required ssl_ca = _.example.com.issuer.crt ssl_cert = .example.com.crt ssl_cipher_list = ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:DHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384 ssl_dh = # hidden, use -P to show it ssl_key = # hidden, use -P to show it ssl_prefer_server_ciphers = yes userdb { args = /etc/dovecot/local_sql_users.conf default_fields = uid=foo_virtmail gid=foo_virtmail home=/foo_data/mail/%d/%n driver = sql } protocol lmtp { mail_plugins = notify replication push_notification sieve postmaster_address = foo@foobar.com } protocol lda { deliver_log_format = msgid=%m: %$ mail_plugins = notify replication push_notification sieve postmaster_address = postmaster quota_full_tempfail = yes rejection_reason = Your message to <%t> was automatically rejected:%n%r } protocol imap { mail_max_userip_connections = 20 mail_plugins = notify replication push_notification imap_sieve }