dovecot -n
# 2.3.3 (dcead646b): /etc/dovecot/dovecot.conf
# OS: Linux 4.14.73 x86_64 Slackware 14.2+
glibc-2.28-x86_64
gcc-8.2.0-x86_64
Filesystem: ext4

telnet localhost imap
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
* BYE Disconnected: Auth process broken
Connection closed by foreign host.

cat /var/log/maillog
Oct  3 08:15:44 mail dovecot: auth: Fatal: master: service(auth): child 9586 killed with signal 11 (core dumped)
Oct  3 08:15:44 mail dovecot: master: Error: service(auth): command startup failed, throttling for 60 secs
Oct  3 08:15:44 mail dovecot: imap-login: Disconnected: Auth process broken (disconnected before auth was ready, waited 0 secs): user=<>, rip=127.0.0.1, lip=127.0.0.1, secured, session=<yk1YIUx3ZuN/AAAB>
Oct  3 08:15:44 mail dovecot: imap-login: Warning: Timeout leak: 0x7fba6c273870 (auth-server-connection.c:397)

gdb /usr/local/libexec/dovecot/auth /tmp/cores/core.auth.9586.mail.1538543744
GNU gdb (GDB) 8.2
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Reading symbols from /usr/local/libexec/dovecot/auth...done.
[New LWP 9586]
Core was generated by `dovecot/auth'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0  0x00007f93c1ff4646 in __strcmp_ssse3 () from /lib64/libc.so.6
(gdb) bt full
#0  0x00007f93c1ff4646 in __strcmp_ssse3 () from /lib64/libc.so.6
No symbol table info available.
#1  0x000055574dbb58e8 in password_scheme_register_crypt () at password-scheme-crypt.c:190
        i = 0
        crypted = <optimized out>
        __func__ = <optimized out>
#2  0x000055574dbb543c in password_schemes_init () at password-scheme.c:874
        i = <optimized out>
#3  0x000055574db91936 in main_preinit () at main.c:185
        mod_set = {abi_version = 0x0, binary_name = 0x0, setting_name = 0x7ffe57a5d998 "\253ݥW\376\177", filter_callback = 0x7ffe57a5d9a8,
          filter_context = 0x7ffe57a5d8d0, require_init_funcs = false, debug = false, ignore_dlopen_errors = true, ignore_missing = true}
        services = <optimized out>
        mod_set = <optimized out>
        services = <optimized out>
#4  main (argc=<optimized out>, argv=<optimized out>) at main.c:392
        c = <optimized out>