Postfix/smtpd: warning and error

Hello,
oh the email log server I have two warning:

postfix/smtpd[47719]: warning: connect to Milter service inet:127.0.0.1:8891: Connection refused

and

postfix/smtpd[46022]: error: open database /etc/aliases.db: No such file or directory

VERSION (fresh install):

Current Version: 2.3
Build: 4
Current Commit: 6eeaca15d3bb0defa1ef76bbaec642fb82230570
Latest Version: 2.3
Latest Build: 4
Latest Commit: 5512f136775fc22b1baf669b801dd6f69821ff20

EMAIL LOG (on Cyberpanel)

May 6 21:52:53 vps-stefano postfix[42953]: Postfix is using backwards-compatible default settings
May 6 21:52:53 vps-stefano postfix[42953]: See Postfix Backwards-Compatibility Safety Net for details
May 6 21:52:53 vps-stefano postfix[42953]: To disable backwards compatibility use “postconf compatibility_level=3.6” and “postfix reload”
May 6 21:52:54 vps-stefano postfix/postfix-script[42960]: stopping the Postfix mail system
May 6 21:52:54 vps-stefano postfix/master[38403]: terminating on signal 15
May 6 21:52:54 vps-stefano postfix[42972]: Postfix is using backwards-compatible default settings
May 6 21:52:54 vps-stefano postfix[42972]: See Postfix Backwards-Compatibility Safety Net for details
May 6 21:52:54 vps-stefano postfix[42972]: To disable backwards compatibility use “postconf compatibility_level=3.6” and “postfix reload”
May 6 21:52:54 vps-stefano postfix/postfix-script[43036]: starting the Postfix mail system
May 6 21:52:54 vps-stefano postfix/master[43038]: daemon started – version 3.8.0, configuration /etc/postfix
May 6 21:52:54 vps-stefano dovecot[38311]: master: Warning: Killed with signal 15 (by pid=43042 uid=0 code=kill)
May 6 21:52:55 vps-stefano dovecot[43053]: master: Dovecot v2.3.20 (80a5ac675d) starting up for imap, pop3 (core dumps disabled)
May 6 21:53:39 vps-stefano postfix/smtpd[46022]: error: open database /etc/aliases.db: No such file or directory
May 6 21:53:39 vps-stefano postfix/smtpd[46022]: connect from vps-stefano.novalocal[127.0.0.1]
May 6 21:53:39 vps-stefano postfix/smtpd[46022]: warning: connect to Milter service inet:127.0.0.1:8891: Connection refused
May 6 21:53:39 vps-stefano postfix/trivial-rewrite[46027]: using backwards-compatible default setting append_dot_mydomain=yes to rewrite “VPS-STEFANO” to “VPS-STEFANO.novalocal”
May 6 21:53:39 vps-stefano postfix/trivial-rewrite[46027]: using backwards-compatible default setting append_dot_mydomain=yes to rewrite “VPS-STEFANO” to “VPS-STEFANO.novalocal”
May 6 21:53:39 vps-stefano postfix/smtpd[46022]: B205E2842247: client=vps-stefano.novalocal[127.0.0.1]
May 6 21:53:39 vps-stefano postfix/trivial-rewrite[46027]: using backwards-compatible default setting append_dot_mydomain=yes to rewrite “VPS-STEFANO” to “VPS-STEFANO.novalocal”
May 6 21:53:39 vps-stefano postfix/trivial-rewrite[46027]: using backwards-compatible default setting append_dot_mydomain=yes to rewrite “VPS-STEFANO” to “VPS-STEFANO.novalocal”
May 6 21:53:39 vps-stefano postfix/cleanup[46028]: B205E2842247: message-id=20230506195339.B205E2842247@vps-stefano.novalocal
May 6 21:53:39 vps-stefano postfix/qmgr[43040]: B205E2842247: from=root@VPS-STEFANO.novalocal, size=4770, nrcpt=1 (queue active)
May 6 21:53:39 vps-stefano postfix/smtpd[46022]: disconnect from vps-stefano.novalocal[127.0.0.1] ehlo=1 mail=1 rcpt=1 data=1 commands=4
May 6 21:53:40 vps-stefano postfix/smtp[46029]: B205E2842247: to=ste.fattori@gmail.com, relay=gmail-smtp-in.l.google.com[108.177.15.26]:25, delay=0.49, delays=0.03/0.02/0.2/0.24, dsn=5.7.1, status=bounced (host gmail-smtp-in.l.google.com[108.177.15.26] said: 550-5.7.1 [80.211.120.70 12] Our system has detected that this message is 550-5.7.1 likely unsolicited mail. To reduce the amount of spam sent to Gmail, 550-5.7.1 this message has been blocked. Please visit 550-5.7.1 Why has Gmail blocked my messages? - Gmail Help 550 5.7.1 for more information. n17-20020a5d4c51000000b0030647d1f349si2613754wrt.715 - gsmtp (in reply to end of DATA command))
May 6 21:53:40 vps-stefano postfix/cleanup[46028]: 372572842248: message-id=20230506195340.372572842248@vps-stefano.novalocal
May 6 21:53:40 vps-stefano postfix/qmgr[43040]: 372572842248: from=<>, size=7529, nrcpt=1 (queue active)
May 6 21:53:40 vps-stefano postfix/bounce[46059]: B205E2842247: sender non-delivery notification: 372572842248
May 6 21:53:40 vps-stefano postfix/qmgr[43040]: B205E2842247: removed
May 6 21:53:40 vps-stefano postfix/smtp[46029]: 372572842248: to=root@VPS-STEFANO.novalocal, relay=none, delay=0.02, delays=0.01/0/0.01/0, dsn=5.4.4, status=bounced (Host or domain name not found. Name service error for name=VPS-STEFANO.novalocal type=AAAA: Host not found)
May 6 21:53:40 vps-stefano postfix/qmgr[43040]: 372572842248: removed
May 6 21:53:42 vps-stefano postfix[46063]: Postfix is using backwards-compatible default settings
May 6 21:53:42 vps-stefano postfix[46063]: See Postfix Backwards-Compatibility Safety Net for details
May 6 21:53:42 vps-stefano postfix[46063]: To disable backwards compatibility use “postconf compatibility_level=3.6” and “postfix reload”
May 6 21:53:42 vps-stefano postfix/postfix-script[46070]: stopping the Postfix mail system
May 6 21:53:42 vps-stefano postfix/master[43038]: terminating on signal 15
May 6 21:53:42 vps-stefano postfix[46082]: Postfix is using backwards-compatible default settings
May 6 21:53:42 vps-stefano postfix[46082]: See Postfix Backwards-Compatibility Safety Net for details
May 6 21:53:42 vps-stefano postfix[46082]: To disable backwards compatibility use “postconf compatibility_level=3.6” and “postfix reload”
May 6 21:53:43 vps-stefano postfix/postfix-script[46147]: starting the Postfix mail system
May 6 21:53:43 vps-stefano postfix/master[46149]: daemon started – version 3.8.0, configuration /etc/postfix
May 6 21:53:43 vps-stefano dovecot[43053]: master: Warning: Killed with signal 15 (by pid=46153 uid=0 code=kill)
May 6 21:53:44 vps-stefano dovecot[46163]: master: Dovecot v2.3.20 (80a5ac675d) starting up for imap, pop3 (core dumps disabled)
May 6 21:56:57 vps-stefano postfix/smtpd[47719]: error: open database /etc/aliases.db: No such file or directory
May 6 21:56:57 vps-stefano postfix/smtpd[47719]: connect from vps-stefano.novalocal[127.0.0.1]
May 6 21:56:57 vps-stefano postfix/smtpd[47719]: warning: connect to Milter service inet:127.0.0.1:8891: Connection refused
May 6 21:56:57 vps-stefano postfix/trivial-rewrite[47724]: using backwards-compatible default setting append_dot_mydomain=yes to rewrite “VPS-STEFANO” to “VPS-STEFANO.novalocal”
May 6 21:56:57 vps-stefano postfix/trivial-rewrite[47724]: using backwards-compatible default setting append_dot_mydomain=yes to rewrite “VPS-STEFANO” to “VPS-STEFANO.novalocal”
May 6 21:56:57 vps-stefano postfix/smtpd[47719]: NOQUEUE: reject: RCPT from vps-stefano.novalocal[127.0.0.1]: 550 5.1.1 email@stefanofattori.it: Recipient address rejected: User unknown in virtual mailbox table; from=root@VPS-STEFANO to=email@stefanofattori.it proto=ESMTP helo=<vps-stefano.novalocal>
May 6 21:56:57 vps-stefano postfix/smtpd[47719]: lost connection after RSET from vps-stefano.novalocal[127.0.0.1]
May 6 21:56:57 vps-stefano postfix/smtpd[47719]: disconnect from vps-stefano.novalocal[127.0.0.1] ehlo=1 mail=1 rcpt=0/1 rset=1 commands=3/4

How can I resolve them?

Thanks a lot
Stefano