SMTP error(451): Failed to add recipient

[McIsTheLimit]

What do your dovecot and mail logs show? This should have been one of the first things you checked

Code:

Jan 25 11:32:07 admin postfix/trivial-rewrite[22540]: warning: proxy:mysql:/etc/sentora/configs/postfix/mysql-virtual_alias_maps.cf: table lookup problem
Jan 25 11:32:07 admin postfix/trivial-rewrite[22540]: warning: virtual_alias_domains lookup failure
Jan 25 11:32:07 admin postfix/trivial-rewrite[22540]: warning: proxy:mysql:/etc/sentora/configs/postfix/mysql-virtual_alias_maps.cf: table lookup problem
Jan 25 11:32:07 admin postfix/trivial-rewrite[22540]: warning: virtual_alias_domains lookup failure
Jan 25 11:32:07 admin postfix/smtpd[25021]: NOQUEUE: reject: RCPT from localhost.localdomain[127.0.0.1]: 451 4.3.0 <admin@synchrocraft.net>: Temporary lookup failure; from=<mcisthelimit@synchrocraft.net> to=<admin@synchrocraft.net> proto=ESMTP helo=<admin.synchrocraft.us>
Jan 25 11:32:07 admin postfix/smtpd[25021]: disconnect from localhost.localdomain[127.0.0.1]
Jan 25 11:32:07 admin postfix/pickup[5180]: warning: E877265B19: message has been queued for 7 days
Jan 25 11:32:07 admin postfix/pickup[5180]: E877265B19: uid=0 from=<root>
Jan 25 11:32:07 admin postfix/cleanup[25025]: warning: proxy:mysql:/etc/sentora/configs/postfix/mysql-virtual_alias_maps.cf lookup error for "root@admin.synchrocraft.us"
Jan 25 11:32:07 admin postfix/cleanup[25025]: warning: E877265B19: virtual_alias_maps map lookup problem for root@admin.synchrocraft.us -- message not accepted, try again later
Jan 25 11:32:08 admin postfix/pickup[5180]: warning: E8C0F65B19: message has been queued for 34 days
Jan 25 11:32:08 admin postfix/pickup[5180]: E8C0F65B19: uid=33 from=<synchrocraft@gmail.com>

This is just from today in the Mail.log