Emails to multiple recipients on same server not getting delivered

[Steve Dondley]

When I send an email to a single user on a server, it is received by the 
user without a problem. But when sending to multiple users, the emails 
disappear into a black hole. The logs contain no errors and indicate the 
emails were sent:

Apr  5 13:10:29 email postfix/pipe[31703]: F3A912027D: 
to=<pete2 at example.org>, relay=spamassassin, delay=1.6, 
delays=0.12/0/0/1.5, dsn=2.0.0, status=sent (delivered via spamassassin 
service (X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on 
email.example.org X-Spam-Level:  X-Spam-Stat))

Apr  5 13:10:29 email postfix/pipe[31703]: F3A912027D: 
to=<pete3 at example.org>, relay=spamassassin, delay=1.6, 
delays=0.12/0/0/1.5, dsn=2.0.0, status=sent (delivered via spamassassin 
service (X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on 
email.example.org X-Spam-Level:  X-Spam-Stat))

However, when I check the inboxes for the recipients, the email is 
nowhere to be found. I tried lifting the receiving/concurrent limits but 
to no effect. I have other servers with very similar configurations to 
this one but I'm not having issues with them. lmtp is the local delivery 
agent.

My postconf:

alias_maps = hash:/etc/aliases
biff = no
broken_sasl_auth_clients = yes
command_directory = /usr/sbin
compatibility_level = 2
daemon_directory = /usr/lib/postfix/sbin
data_directory = /var/lib/postfix
debugger_command = PATH=/bin:/usr/bin:/usr/local/bin:/usr/X11R6/bin ddd 
$daemon_directory/$process_name $process_id & sleep 5
default_destination_concurrency_limit = 5
home_mailbox = Maildir/
inet_interfaces = all
lmtp_destination_concurrency_limit = 5
lmtp_destination_recipient_limit = 5
local_destination_concurrency_limit = 5
local_destination_recipient_limit = 5
mail_owner = postfix
mailbox_size_limit = 3145728000
mailbox_transport = lmtp:unix:private/dovecot-lmtp
mailq_path = /usr/bin/mailq
message_size_limit = 26214400
milter_default_action = accept
milter_protocol = 6
mydestination = $myhostname localhost.$mydomain localhost $mydomain
mydomain = example.org
myhostname = email.example.org
mynetworks_style = subnet
myorigin = example.org
non_smtpd_milters = $smtpd_milters
policyd-spf_time_limit = 3600
recipient_bcc_maps = pcre:/etc/postfix/recipient_bcc
recipient_delimiter = +
sendmail_path = /usr/sbin/sendmail
setgid_group = postdrop
smtp_tls_note_starttls_offer = yes
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache
smtp_use_tls = yes
smtpd_banner = $myhostname ESMTP
smtpd_milters = unix:/opendkim/opendkim.sock
smtpd_recipient_restrictions = permit_mynetworks, 
permit_sasl_authenticated, reject_unauth_destination, 
check_policy_service unix:private/policyd-spf
smtpd_relay_restrictions = permit_mynetworks permit_sasl_authenticated 
defer_unauth_destination
smtpd_sasl_auth_enable = yes
smtpd_sasl_local_domain = $myhostname
smtpd_sasl_path = private/auth
smtpd_sasl_security_options = noanonymous
smtpd_sasl_type = dovecot
smtpd_sender_login_maps = pcre:/etc/postfix/login_maps.pcre
smtpd_sender_restrictions = reject_authenticated_sender_login_mismatch
smtpd_tls_cert_file = 
/etc/letsencrypt/live/email.example.org/fullchain.pem
smtpd_tls_key_file = /etc/letsencrypt/live/email.example.org/privkey.pem
smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
smtpd_use_tls = yes
unknown_local_recipient_reject_code = 550
virtual_alias_maps = hash:/etc/postfix/virtual
virtual_mailbox_limit = 26214400
virtual_transport = lmtp:unix:private/dovecot-lmtp

And doveconf:

# 2.3.4.1 (f79e8e7e4): /etc/dovecot/dovecot.conf
# Pigeonhole version 0.5.4 ()
# OS: Linux 4.19.0-14-cloud-amd64 x86_64 Debian 10.9
# Hostname: email.example.org
auth_mechanisms = plain login
auth_username_format = %Ln
disable_plaintext_auth = no
mail_debug = yes
mail_location = maildir:~/Maildir
mail_privileged_group = mail
managesieve_notify_capability = mailto
managesieve_sieve_capability = fileinto reject envelope 
encoded-character vacation subaddress comparator-i;ascii-numeric 
relational regex imap4flags copy include variables body enotify 
environment mailbox date index ihave duplicate mime foreverypart 
extracttext
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 = /etc/dovecot/aliases
   driver = passwd-file
}
passdb {
   driver = pam
}
plugin {
   recipient_delimiter = +
   sieve = file:~/sieve;active=~/.dovecot.sieve
   sieve_default = /var/lib/dovecot/sieve/default.sieve
   sieve_default_name = Defaults
   sieve_global = /var/lib/dovecot/sieve
}
pop3_client_workarounds = outlook-no-nuls
protocols = " imap lmtp sieve pop3 sieve"
service auth {
   unix_listener /var/spool/postfix/private/auth {
     group = postfix
     mode = 0666
     user = postfix
   }
   unix_listener auth-userdb {
     mode = 0666
   }
}
service imap-login {
   inet_listener imap {
     port = 143
   }
   inet_listener imaps {
     port = 993
     ssl = yes
   }
}
service imap {
   client_limit = 1
}
service lmtp {
   client_limit = 1
   unix_listener /var/spool/postfix/private/dovecot-lmtp {
     group = postfix
     mode = 0600
     user = postfix
   }
}
service managesieve-login {
   inet_listener sieve {
     port = 4190
   }
}
service pop3-login {
   inet_listener pop3s {
     port = 995
     ssl = yes
   }
}
service submission-login {
   inet_listener submission {
     port = 587
   }
}
ssl_cert = </etc/letsencrypt/live/email.example.org/fullchain.pem
ssl_client_ca_dir = /etc/ssl/certs
ssl_dh = # hidden, use -P to show it
ssl_key = # hidden, use -P to show it
userdb {
   driver = passwd
}
protocol lmtp {
   mail_plugins = " sieve"
}