Bug#1012431: exim4: Exim does not deliver local mail immediately through pipe transport

[Kamil Jonca]

Package: exim4
Version: exim4-daemon-light
Severity: normal
X-Debbugs-Cc: kjonca at poczta.onet.pl

I have configured exim to deliver mail via dovecot-lda with pipe transport.

Recently I found that mails between two different local user are not delivered immediately but, during first deliver exim got "Resource temporarily unavailable"
and message is put to queue and delivered during queue run.

i.e. 
when I try:

======
echo bla|sudo -u logcheck mail kjonca
=====

i got in logs:
============
2022-06-07 06:24:13.531 [2774788] 1nyQlJ-00Bdqe-FA <= logcheck at alfa.kjonca U=logcheck P=local S=436 M8S=0 RT=0.004s id*=E1nyQlJ-00Bdqe-FA at alfa.kjonca from <logcheck at alfa.kjonca> for kjonca
2022-06-07 06:24:13.551 [2774789] 1nyQlJ-00Bdqe-FA == kjonca at alfa.kjonca R=dovecot T=dovecot_pipe defer (0) DT=0.003s: Failed to create child process for dovecot_pipe transport: Resource temporarily unavailable
============
and message is in queue

user root have no this problem:
ie 

=====
echo bla|sudo mail kjonca
=====

makes immediately delivery.
How can I debug this?
KJ


-- System Information:
Debian Release: bookworm/sid
  APT prefers unstable
  APT policy: (500, 'unstable'), (500, 'oldstable')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 5.17.0-3-amd64 (SMP w/12 CPU threads; PREEMPT)
Locale: LANG=pl_PL.UTF-8, LC_CTYPE=pl_PL.UTF-8 (charmap=UTF-8), LANGUAGE not set
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages exim4 depends on:
ii  debconf [debconf-2.0]  1.5.79
ii  exim4-base             4.95-6
ii  exim4-daemon-light     4.95-6

exim4 recommends no packages.

exim4 suggests no packages.