Server certificate verification error with Dovecot 2.3.2.1

[Robert Gill]

I'm attempting to upgrade my Dovecot installation to 2.3.2.1. My SSL
certificate authority provides a bundle containing their CA, plus
intermediate CAs, which I configure using the 'ssl_ca' option. The
comments in the configuration file say to only set this when you're
requiring client certificates, which I'm not, but fetchmail complains
with a "Server certificate verification error, Broken certificate chain"
error if that setting is not set. This works fine with Dovecot 2.2.34.

After upgrading to 2.3.2.1, fetchmail throws that error whether 'ssl_ca'
is set or not. Dovecot 2.3.2.1 reports the error

  SSL routines:ssl3_read_bytes:tlsv1 alert unknown ca: SSL alert number 48
  
in the logs when attempting the TLS handshake. The permissions on the CA
bundle haven't changed and should still be readable by Dovecot.

I'm running Gentoo Linux on x86_64 and mail is stored on an ext4 file
system. I'm attaching my config files for both Dovecot 2.2.34 and
Dovecot 2.3.2.1.
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# 2.2.34 (874deae): /etc/dovecot/dovecot.conf
# OS: Linux 4.9.95-gentoo x86_64 Gentoo Base System release 2.4.1 
# Hostname: hermes.ultramedonline.com
mail_access_groups = mail
mail_location = mbox:~/mail:INBOX=/var/spool/mail/%n
mail_privileged_group = mail
mbox_write_locks = fcntl
namespace inbox {
  inbox = yes
  location = 
  mailbox Drafts {
    special_use = \Drafts
  }
  mailbox Junk {
    special_use = \Junk
  }
  mailbox Sent {
    special_use = \Sent
  }
  mailbox "Sent Messages" {
    special_use = \Sent
  }
  mailbox Trash {
    special_use = \Trash
  }
  prefix = 
}
passdb {
  args = *
  driver = pam
}
passdb {
  args = scheme=sha512-crypt username_format=%n /etc/mail/passwd
  driver = passwd-file
}
ssl_ca = </etc/ssl/local/certs/gd_bundle-g2-g1.crt
ssl_cert = </etc/ssl/local/certs/wildcard.crt
ssl_cipher_list = DEFAULT:!EXPORT:!LOW:!MEDIUM:!MD5
ssl_dh_parameters_length = 4096
ssl_key =  # hidden, use -P to show it
userdb {
  driver = passwd
}
userdb {
  args = username_format=%n /etc/mail/passwd
  default_fields = uid=vmail gid=vmail home=/var/spool/vmail/%n
  driver = passwd-file
}
-------------- next part --------------
# 2.3.2.1 (0719df592): /etc/dovecot/dovecot.conf
# OS: Linux 4.9.95-gentoo x86_64 Gentoo Base System release 2.4.1 
# Hostname: hermes.ultramedonline.com
mail_access_groups = mail
mail_location = mbox:~/mail:INBOX=/var/spool/mail/%n
mail_privileged_group = mail
mbox_write_locks = fcntl
namespace inbox {
  inbox = yes
  location = 
  mailbox Drafts {
    special_use = \Drafts
  }
  mailbox Junk {
    special_use = \Junk
  }
  mailbox Sent {
    special_use = \Sent
  }
  mailbox "Sent Messages" {
    special_use = \Sent
  }
  mailbox Trash {
    special_use = \Trash
  }
  prefix = 
}
passdb {
  args = *
  driver = pam
}
passdb {
  args = scheme=sha512-crypt username_format=%n /etc/mail/passwd
  driver = passwd-file
}
ssl_ca = </etc/ssl/local/certs/gd_bundle-g2-g1.crt
ssl_cert = </etc/ssl/local/certs/wildcard.crt
ssl_cipher_list = DEFAULT:!EXPORT:!LOW:!MEDIUM:!MD5
ssl_dh =  # hidden, use -P to show it
ssl_key =  # hidden, use -P to show it
userdb {
  driver = passwd
}
userdb {
  args = username_format=%n /etc/mail/passwd
  default_fields = uid=vmail gid=vmail home=/var/spool/vmail/%n
  driver = passwd-file
}