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@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@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 =