Bug#979965: milter-greylist exits after running for a few minutes

[Michael Grant <mgrant@grant.org>]

Package: milter-greylist
Version: 4.6.2-2
Severity: important

Dear Maintainer,

After update to 4.6.2-2, milter-greylist runs for a few minutes
processing greylist requests then exits.  No error in the daemon.log.
Daemon restarts with systemd over and over.

Starting milter-greylist by hand using strace shows this just before
it dies:

poll([{fd=3, events=POLLIN|POLLPRI}], 1, 5000) = 0 (Timeout)
poll([{fd=3, events=POLLIN|POLLPRI}], 1, 5000) = 0 (Timeout)
poll([{fd=3, events=POLLIN|POLLPRI}], 1, 5000) = 0 (Timeout)
poll([{fd=3, events=POLLIN|POLLPRI}], 1, 5000) = 1 ([{fd=3,
revents=POLLIN}])
accept(3, {sa_family=AF_UNIX}, [2])     = 10
fcntl(10, F_GETFD)                      = 0
fcntl(10, F_SETFD, FD_CLOEXEC)          = 0
setsockopt(10, SOL_SOCKET, SO_KEEPALIVE, [1], 4) = 0
futex(0x7f0f22c221a4, FUTEX_WAKE_PRIVATE, 1) = 1
poll([{fd=3, events=POLLIN|POLLPRI}], 1, 5000) = 0 (Timeout)
poll([{fd=3, events=POLLIN|POLLPRI}], 1, 5000 <unfinished ...>) = ?
+++ exited with 71 +++

Previous version of milter-greylist on debian/testing was working fine
without this issue.

-- System Information:
Debian Release: bullseye/sid
  APT prefers testing
  APT policy: (750, 'testing'), (50, 'unstable'), (1, 'experimental')
Architecture: amd64 (x86_64)

Kernel: Linux 5.9.6-x86_64-linode139 (SMP w/2 CPU threads)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8) (ignored: LC_ALL set to en_US.UTF-8), LANGUAGE not set
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages milter-greylist depends on:
ii  adduser              3.118
ii  init-system-helpers  1.60
ii  libc6                2.31-6
ii  libcurl4             7.74.0-1
ii  libgeoip1            1.6.12-7
ii  libmilter1.0.1       8.15.2-20
ii  libopendkim11        2.11.0~beta2-4
ii  libspf2-2            1.2.10-7+b7
ii  lsb-base             11.1.0

Versions of packages milter-greylist recommends:
ii  sendmail  8.15.2-20

milter-greylist suggests no packages.

-- Configuration Files:
/etc/default/milter-greylist changed [not included]
/etc/milter-greylist/greylist.conf changed [not included]

-- no debconf information