title: Strange errors in postfix mail.warn log
body: <p>How to avoid getting strange records in the mail.warn file?
  I started to receive it after Debian upgrade from jessie to stretch and postfix upgrade from 2.11.3 to 3.1.8. It is generated once, just after the system reboot.</p>
  
  <p>Despite the strange errors recorded in mail.warn file, it seems that postfix works fine.</p>
  
  <p>My current environment is the following:
  Debian 9 <code>stretch</code>
  Postfix 3.1.8
  Dovecot 2.2.27 (c0f36b0)
  10.1.23-MariaDB-9+deb9u1</p>
  
  <pre><code>Mar 18 12:57:52 jessie postfix/proxymap[862]: warning: connect to mysql server localhost: Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (2 "No such file or directory")
  Mar 18 12:57:52 jessie postfix/cleanup[861]: warning: proxy:mysql:/etc/postfix/virtual_alias_maps.cf lookup error for "email@example.com"
  Mar 18 12:57:52 jessie postfix/cleanup[861]: warning: 3B61C40601: virtual_alias_maps map lookup problem for email@example.com -- message not accepted, try again later
  Mar 18 12:57:54 jessie postfix/cleanup[861]: warning: proxy:mysql:/etc/postfix/virtual_alias_maps.cf lookup error for "email@example.com"
  Mar 18 12:57:54 jessie postfix/cleanup[861]: warning: 7FA7542CC4: virtual_alias_maps map lookup problem for email@example.com -- message not accepted, try again later
  Mar 18 12:57:54 jessie postfix/cleanup[861]: warning: proxy:mysql:/etc/postfix/virtual_alias_maps.cf lookup error for "email@example.com"
  Mar 18 12:57:54 jessie postfix/cleanup[861]: warning: 8017A42CC4: virtual_alias_maps map lookup problem for email@example.com -- message not accepted, try again later
  Mar 18 12:58:51 jessie postfix/cleanup[861]: warning: proxy:mysql:/etc/postfix/virtual_alias_maps.cf lookup error for "email@example.com"
  Mar 18 12:58:51 jessie postfix/cleanup[861]: warning: 889C33FAA1: virtual_alias_maps map lookup problem for email@example.com -- message not accepted, try again later
  Mar 18 12:58:51 jessie postfix/cleanup[861]: warning: proxy:mysql:/etc/postfix/virtual_alias_maps.cf lookup error for "email@example.com"
  Mar 18 12:58:51 jessie postfix/cleanup[861]: warning: 894A13FAA1: virtual_alias_maps map lookup problem for email@example.com -- message not accepted, try again later
  </code></pre>
  
  <p>postfix main.cf:</p>
  
  <pre><code>alias_database = hash:/etc/aliases
  alias_maps = hash:/etc/aliases
  anvil_rate_time_unit = 60s
  append_dot_mydomain = no
  biff = no
  compatibility_level = 1
  home_mailbox = Maildir/
  inet_interfaces = all
  inet_protocols = ipv4
  local_recipient_maps = $virtual_mailbox_maps
  local_transport = virtual
  mailbox_command =
  mailbox_size_limit = 0
  mime_header_checks = regexp:/etc/postfix/block_attachments
  mydestination = localhost
  myhostname = waw.homeip.net
  mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
  myorigin = /etc/mailname
  readme_directory = no
  recipient_delimiter = +
  relay_domains = $mydestination
  relayhost =
  smtp_tls_loglevel = 1
  smtp_tls_mandatory_protocols = !SSLv2,!SSLv3
  smtp_tls_protocols = !SSLv2,!SSLv3
  smtp_tls_security_level = may
  smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache
  smtpd_banner = $myhostname ESMTP $mail_name (Debian/GNU)
  smtpd_client_connection_count_limit = 10
  smtpd_client_connection_rate_limit = 5
  smtpd_client_restrictions = permit_mynetworks, permit_sasl_authenticated, reject_unauth_pipelining, reject_rbl_client zen.spamhaus.org
  smtpd_error_sleep_time = 5s
  smtpd_hard_error_limit = 10
  smtpd_helo_required = yes
  smtpd_helo_restrictions = permit_mynetworks, permit_sasl_authenticated, reject_invalid_helo_hostname, reject_non_fqdn_helo_hostname, check_helo_access hash:/etc/postfix/helo_access
  smtpd_recipient_restrictions = permit_sasl_authenticated, permit_mynetworks, reject_unauth_destination, reject_invalid_hostname, reject_non_fqdn_hostname, reject_non_fqdn_sender, reject_non_fqdn_recipient, reject_unknown_sender_domain, reject_unknown_recipient_domain, check_client_access hash:/etc/postfix/rbl_override, reject_rbl_client zen.spamhaus.org, reject_rbl_client cbl.abuseat.org, permit
  smtpd_relay_restrictions = permit_sasl_authenticated, permit_mynetworks, reject_unauth_destination, reject_invalid_hostname, reject_non_fqdn_hostname, reject_non_fqdn_sender, reject_non_fqdn_recipient, reject_unknown_sender_domain, reject_unknown_recipient_domain, check_client_access hash:/etc/postfix/rbl_override, reject_rbl_client zen.spamhaus.org, reject_rbl_client cbl.abuseat.org, permit
  smtpd_sasl_auth_enable = yes
  smtpd_sasl_path = private/auth
  smtpd_sasl_type = dovecot
  smtpd_soft_error_limit = 5
  smtpd_tls_auth_only = yes
  smtpd_tls_cert_file = /etc/letsencrypt/live/waw.homeip.net/fullchain.pem
  smtpd_tls_dh1024_param_file = /etc/ssl_test/dhparam/dhparams.pem
  smtpd_tls_exclude_ciphers = aNULL, eNULL, EXPORT, DES, RC4, MD5, PSK, aECDH, EDH-DSS-DES-CBC3-SHA, EDH-RSA-DES-CDC3-SHA, KRB5-DE5, CBC3-SHA
  smtpd_tls_key_file = /etc/letsencrypt/live/waw.homeip.net/privkey.pem
  smtpd_tls_loglevel = 1
  smtpd_tls_mandatory_protocols = !SSLv2,!SSLv3
  smtpd_tls_protocols = !SSLv2,!SSLv3
  smtpd_tls_security_level = may
  smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
  smtpd_use_tls = yes
  transport_maps = hash:/etc/postfix/transport
  virtual_alias_maps = proxy:mysql:/etc/postfix/virtual_alias_maps.cf
  virtual_gid_maps = static:5000
  virtual_mailbox_base = /home/vmail
  virtual_mailbox_domains = proxy:mysql:/etc/postfix/virtual_mailbox_domains.cf
  virtual_mailbox_limit = 512000000
  virtual_mailbox_maps = proxy:mysql:/etc/postfix/virtual_mailbox_maps.cf
  virtual_minimum_uid = 5000
  virtual_transport = virtual
  virtual_uid_maps = static:5000
  </code></pre>
  
  <p>virtual_alias_maps.cf</p>
  
  <pre><code>user = postfix_user
  password = password
  hosts = localhost
  dbname = postfix_db
  table = alias
  select_field = goto
  where_field = address
  </code></pre>