<admin@domain2.tld>: host 127.0.0.25[127.0.0.25] said: 550 5.1.1
<admin@domain2.tld>: Recipient address rejected: User unknown in virtual
mailbox table (in reply to RCPT TO command)

mail server a:

alias_database = hash:/etc/aliases
alias_maps = $alias_database
broken_sasl_auth_clients = yes
command_directory = /usr/local/sbin
config_directory = /usr/local/etc/postfix
daemon_directory = /usr/local/libexec/postfix
debug_peer_level = 2
html_directory = no
mail_owner = postfix
mailq_path = /usr/local/bin/mailq
manpage_directory = /usr/local/man
masquerade_domains = mx.blitzpost.com blitzpost.com
mydestination = $myhostname, localhost.$mydomain, localhost
myhostname = mx.blitzpost.com
mynetworks = 168.100.189.0/28, 127.0.0.0/8, 192.168.1.0/24
mynetworks_style = subnet
myorigin = domain1.tld
newaliases_path = /usr/local/bin/newaliases
queue_directory = /var/spool/postfix
readme_directory = no
relayhost = 192.168.1.10
sample_directory = /usr/local/etc/postfix
sendmail_path = /usr/local/sbin/sendmail
setgid_group = maildrop
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = mysql:/usr/local/etc/postfix/cf/mysql_virtual_mailbox_maps.cf
smtp_sasl_security_options = noanonymous
smtpd_banner = $myhostname ESMTP $mail_name
smtpd_recipient_restrictions = permit_mynetworks, permit_sasl_authenticated, reject_unauth_destination
smtpd_sasl_exceptions_networks = $mynetworks
unknown_local_recipient_reject_code = 550
virtual_alias_maps = proxy:mysql:$config_directory/cf/mysql_virtual_alias_maps.cf
virtual_gid_maps = static:125
virtual_mailbox_base = /data
virtual_mailbox_domains = proxy:mysql:$config_directory/cf/mysql_virtual_domains_maps.cf
virtual_mailbox_maps = proxy:mysql:$config_directory/cf/mysql_virtual_mailbox_maps.cf
virtual_minimum_uid = 125
virtual_uid_maps = static:125

mail server b:
alias_database = hash:/etc/postfix/aliases
command_directory = /usr/local/sbin
config_directory = /etc/postfix
daemon_directory = /usr/local/libexec/postfix
data_directory = /var/postfix
debug_peer_level = 2
home_mailbox = Maildir/
html_directory = /usr/local/share/doc/postfix/html
inet_protocols = all
mail_owner = _postfix
mailq_path = /usr/local/sbin/mailq
manpage_directory = /usr/local/man
mydestination = $myhostname, localhost.$mydomain, localhost
mydomain = domain2.tld
myhostname = mx.domain2.tld
mynetworks = 127.0.0.0/8, 192.168.1.0/24, 192.168.2.0/24
myorigin = $myhostname
newaliases_path = /usr/local/sbin/newaliases
queue_directory = /var/spool/postfix
readme_directory = /usr/local/share/doc/postfix/readme
sample_directory = /etc/postfix
sendmail_path = /usr/local/sbin/sendmail
setgid_group = _postdrop
smtpd_banner = $myhostname ESMTP $mail_name
unknown_local_recipient_reject_code = 550
virtual_alias_maps = mysql:/etc/postfix/mysql_virtual_alias_maps.cf
virtual_gid_maps = static:2000
virtual_mailbox_base = /var/mail
virtual_mailbox_domains = mysql:/etc/postfix/mysql_virtual_domains.cf
virtual_mailbox_maps = mysql:/etc/postfix/mysql_virtual_mailboxes.cf
virtual_minimum_uid = 2000
virtual_uid_maps = static:2000