Looks like you have two versions installed and are mixing them up.

I checked and only one binary is on the system. I took a look in the directory /usr/local/lib/dovecot/doveadm/ and it appears the upgrade rebuilt all libraries EXCEPT zlib. Any ideas?

-rw-r--r-- 1 root root 125910 Jul 22 10:58 lib10_doveadm_acl_plugin.a -rwxr-xr-x 1 root root 1070 Jul 22 10:58 lib10_doveadm_acl_plugin.la -rwxr-xr-x 1 root root 88190 Jul 22 10:58 lib10_doveadm_acl_plugin.so -rw-r--r-- 1 root root 54812 Jul 22 10:58 lib10_doveadm_expire_plugin.a -rwxr-xr-x 1 root root 1091 Jul 22 10:58 lib10_doveadm_expire_plugin.la -rwxr-xr-x 1 root root 44763 Jul 22 10:58 lib10_doveadm_expire_plugin.so -rw-r--r-- 1 root root 89116 Jul 22 10:58 lib10_doveadm_quota_plugin.a -rwxr-xr-x 1 root root 1084 Jul 22 10:58 lib10_doveadm_quota_plugin.la -rwxr-xr-x 1 root root 61137 Jul 22 10:58 lib10_doveadm_quota_plugin.so -rw-r--r-- 1 root root 369576 Jul 22 10:47 lib10_doveadm_sieve_plugin.a -rwxr-xr-x 1 root root 1248 Jul 22 10:47 lib10_doveadm_sieve_plugin.la -rwxr-xr-x 1 root root 208863 Jul 22 10:47 lib10_doveadm_sieve_plugin.so -rw-r--r-- 1 root root 26166 Apr 9 14:30 lib10_doveadm_zlib_plugin.a -rwxr-xr-x 1 root root 1077 Apr 9 14:30 lib10_doveadm_zlib_plugin.la -rwxr-xr-x 1 root root 25243 Apr 9 14:30 lib10_doveadm_zlib_plugin.so -rw-r--r-- 1 root root 100120 Jul 22 10:58 lib20_doveadm_fts_plugin.a -rwxr-xr-x 1 root root 1070 Jul 22 10:58 lib20_doveadm_fts_plugin.la -rwxr-xr-x 1 root root 65515 Jul 22 10:58 lib20_doveadm_fts_plugin.so

Configure does seem to see it though:

checking zlib.h usability... yes checking zlib.h presence... yes checking for zlib.h... yes checking bzlib.h usability... yes checking bzlib.h presence... yes checking for bzlib.h... yes checking for BZ2_bzdopen in -lbz2... yes