A solution to protect my server

Mar 20 03:04:59 amanet dovecot: auth-worker(117378): pam(roni9@mobime.ma,202.82.20.241,<fFh5BA4Um9/KUhTx>): pam_authenticate() failed: Authentication failure (Password mismatch?)
Mar 20 03:04:57 amanet postfix/smtpd[112530]: disconnect from unknown[23.95.86.92] ehlo=2 starttls=1 auth=0/1 commands=3/4
Mar 20 03:04:57 amanet postfix/smtpd[112530]: lost connection after AUTH from unknown[23.95.86.92]
Mar 20 03:04:57 amanet postfix/smtpd[112530]: warning: unknown[23.95.86.92]: SASL LOGIN authentication failed: authentication failure
Mar 20 03:04:56 amanet dovecot: pop3(transit@emultec.ma)<117379>: Disconnected: Logged out top=0/0, retr=0/0, del=0/5580, size=2384802933
Mar 20 03:04:55 amanet dovecot: pop3-login: Login: user=transit@emultec.ma, method=PLAIN, rip=160.176.111.12, lip=173.212.244.42, mpid=117379, TLS, session=
Mar 20 03:04:53 amanet postfix/smtpd[112530]: warning: connect to Milter service local:/var/run/milter-greylist/milter-greylist.sock: No such file or directory
Mar 20 03:04:53 amanet postfix/smtpd[112530]: connect from unknown[23.95.86.92]
Mar 20 03:04:53 amanet postfix/smtpd[112530]: warning: hostname setily-bmpstnt.mutemeet.net does not resolve to address 23.95.86.92: No address associated with hostname
Mar 20 03:04:53 amanet postfix/smtpd[115745]: disconnect from unknown[23.95.86.92] ehlo=2 starttls=1 auth=0/1 commands=3/4
Mar 20 03:04:53 amanet postfix/smtpd[115745]: lost connection after AUTH from unknown[23.95.86.92]
Mar 20 03:04:53 amanet postfix/smtpd[115745]: warning: unknown[23.95.86.92]: SASL LOGIN authentication failed: authentication failure
Mar 20 03:04:49 amanet postfix/smtpd[115745]: warning: connect to Milter service local:/var/run/milter-greylist/milter-greylist.sock: No such file or directory
Mar 20 03:04:49 amanet postfix/smtpd[115745]: connect from unknown[23.95.86.92]
Mar 20 03:04:49 amanet postfix/smtpd[115745]: warning: hostname setily-bmpstnt.mutemeet.net does not resolve to address 23.95.86.92: No address associated with hostname
Mar 20 03:04:49 amanet postfix/smtpd[115305]: disconnect from unknown[23.95.86.92] ehlo=2 starttls=1 auth=0/1 commands=3/4
Mar 20 03:04:49 amanet postfix/smtpd[115305]: lost connection after AUTH from unknown[23.95.86.92]
Mar 20 03:04:49 amanet postfix/smtpd[115305]: warning: unknown[23.95.86.92]: SASL LOGIN authentication failed: authentication failure
Mar 20 03:04:45 amanet postfix/smtpd[112634]: disconnect from unknown[107.173.177.136] ehlo=2 starttls=1 auth=0/1 commands=3/4
Mar 20 03:04:45 amanet postfix/smtpd[112634]: lost connection after AUTH from unknown[107.173.177.136]
Mar 20 03:04:45 amanet postfix/smtpd[112634]: warning: unknown[107.173.177.136]: SASL LOGIN authentication failed: authentication failure
Mar 20 03:04:45 amanet postfix/smtpd[115305]: warning: connect to Milter service local:/var/run/milter-greylist/milter-greylist.sock: No such file or directory
Mar 20 03:04:44 amanet postfix/smtpd[115305]: connect from unknown[23.95.86.92]
Mar 20 03:04:44 amanet postfix/smtpd[115305]: warning: hostname setily-bmpstnt.mutemeet.net does not resolve to address 23.95.86.92: No address associated with hostname
Mar 20 03:04:42 amanet postfix/smtpd[112634]: warning: connect to Milter service local:/var/run/milter-greylist/milter-greylist.sock: No such file or directory
Mar 20 03:04:42 amanet postfix/smtpd[112634]: connect from unknown[107.173.177.136]
Mar 20 03:04:42 amanet postfix/smtpd[112634]: warning: hostname 107-173-177-136-host.colocrossing.com does not resolve to address 107.173.177.136: No address associated with hostname
Mar 20 03:04:41 amanet postfix/smtpd[112530]: disconnect from unknown[107.173.177.136] ehlo=2 starttls=1 auth=0/1 commands=3/4
Mar 20 03:04:41 amanet postfix/smtpd[112530]: lost connection after AUTH from unknown[107.173.177.136]
Mar 20 03:04:41 amanet postfix/smtpd[112530]: warning: unknown[107.173.177.136]: SASL LOGIN authentication failed: authentication failure
Mar 20 03:04:38 amanet postfix/smtpd[112530]: warning: connect to Milter service local:/var/run/milter-greylist/milter-greylist.sock: No such file or directory
Mar 20 03:04:38 amanet postfix/smtpd[112530]: connect from unknown[107.173.177.136]
Mar 20 03:04:38 amanet postfix/smtpd[112530]: warning: hostname 107-173-177-136-host.colocrossing.com does not resolve to address 107.173.177.136: No address associated with hostname
Mar 20 03:04:37 amanet postfix/smtpd[115745]: disconnect from unknown[107.173.177.136] ehlo=2 starttls=1 auth=0/1 commands=3/4
Mar 20 03:04:37 amanet postfix/smtpd[115745]: lost connection after AUTH from unknown[107.173.177.136]
Mar 20 03:04:37 amanet postfix/smtpd[115745]: warning: unknown[107.173.177.136]: SASL LOGIN authentication failed: authentication failure
Mar 20 03:04:33 amanet postfix/smtpd[115745]: warning: connect to Milter service local:/var/run/milter-greylist/milter-greylist.sock: No such file or directory
Mar 20 03:04:33 amanet postfix/smtpd[115745]: connect from unknown[107.173.177.136]
Mar 20 03:04:33 amanet postfix/smtpd[115745]: warning: hostname 107-173-177-136-host.colocrossing.com does not resolve to address 107.173.177.136: No address associated with hostname
Mar 20 03:04:24 amanet postfix/smtpd[111147]: disconnect from unknown[192.227.144.43] ehlo=1 auth=0/1 commands=1/2
Mar 20 03:04:24 amanet postfix/smtpd[111147]: lost connection after AUTH from unknown[192.227.144.43]
Mar 20 03:04:24 amanet postfix/smtpd[111147]: warning: unknown[192.227.144.43]: SASL LOGIN authentication failed: authentication failure
Mar 20 03:04:21 amanet postfix/smtpd[111147]: warning: connect to Milter service local:/var/run/milter-greylist/milter-greylist.sock: No such file or directory
Mar 20 03:04:21 amanet postfix/smtpd[111147]: connect from unknown[192.227.144.43]
Mar 20 03:04:21 amanet postfix/smtpd[111147]: warning: hostname 192-227-144-43-host.colocrossing.com does not resolve to address 192.227.144.43: No address associated with hostname
Mar 20 03:04:20 amanet postfix/smtpd[111149]: disconnect from unknown[192.227.144.43] ehlo=1 auth=0/1 commands=1/2
Mar 20 03:04:20 amanet postfix/smtpd[111149]: lost connection after AUTH from unknown[192.227.144.43]
Mar 20 03:04:20 amanet postfix/smtpd[111149]: warning: unknown[192.227.144.43]: SASL LOGIN authentication failed: authentication failure
Mar 20 03:04:17 amanet postfix/smtpd[111149]: warning: connect to Milter service local:/var/run/milter-greylist/milter-greylist.sock: No such file or directory
Mar 20 03:04:17 amanet postfix/smtpd[111149]: connect from unknown[192.227.144.43]
Mar 20 03:04:17 amanet postfix/smtpd[111149]: warning: hostname 192-227-144-43-host.colocrossing.com does not resolve to address 192.227.144.43: No address associated with hostname
Mar 20 03:04:15 amanet postfix/smtpd[111147]: disconnect from unknown[192.227.144.43] ehlo=1 auth=0/1 commands=1/2
Mar 20 03:04:15 amanet postfix/smtpd[111147]: lost connection after AUTH from unknown[192.227.144.43]
Mar 20 03:04:15 amanet postfix/smtpd[111147]: warning: unknown[192.227.144.43]: SASL LOGIN authentication failed: authentication failure
Mar 20 03:04:15 amanet postfix/smtpd[115305]: disconnect from unknown[192.210.236.155] ehlo=2 starttls=1 auth=0/1 commands=3/4
Mar 20 03:04:15 amanet postfix/smtpd[115305]: lost connection after AUTH from unknown[192.210.236.155]
Mar 20 03:04:15 amanet postfix/smtpd[115305]: warning: unknown[192.210.236.155]: SASL LOGIN authentication failed: authentication failure
Mar 20 03:04:14 amanet postfix/smtpd[115553]: disconnect from unknown[196.191.150.228] ehlo=2 starttls=1 auth=0/1 commands=3/4
Mar 20 03:04:14 amanet postfix/smtpd[115553]: lost connection after AUTH from unknown[196.191.150.228]
Mar 20 03:04:13 amanet postfix/smtpd[115553]: warning: unknown[196.191.150.228]: SASL LOGIN authentication failed: authentication failure
Mar 20 03:04:13 amanet postfix/smtpd[111147]: warning: connect to Milter service local:/var/run/milter-greylist/milter-greylist.sock: No such file or directory
Mar 20 03:04:12 amanet postfix/smtpd[111147]: connect from unknown[192.227.144.43]
Mar 20 03:04:12 amanet postfix/smtpd[111147]: warning: hostname 192-227-144-43-host.colocrossing.com does not resolve to address 192.227.144.43: No address associated with hostname
Mar 20 03:04:12 amanet postfix/smtpd[115305]: warning: connect to Milter service local:/var/run/milter-greylist/milter-greylist.sock: No such file or directory
Mar 20 03:04:12 amanet postfix/smtpd[115305]: connect from unknown[192.210.236.155]
Mar 20 03:04:12 amanet postfix/smtpd[115305]: warning: hostname 192-210-236-155-host.colocrossing.com does not resolve to address 192.210.236.155: No address associated with hostname
Mar 20 03:04:12 amanet postfix/smtpd[111149]: disconnect from unknown[23.94.82.19] ehlo=1 auth=0/1 commands=1/2
Mar 20 03:04:12 amanet postfix/smtpd[111149]: lost connection after AUTH from unknown[23.94.82.19]
Mar 20 03:04:11 amanet postfix/smtpd[111149]: warning: unknown[23.94.82.19]: SASL LOGIN authentication failed: authentication failure
Mar 20 03:04:09 amanet postfix/smtpd[111149]: warning: connect to Milter service local:/var/run/milter-greylist/milter-greylist.sock: No such file or directory
Mar 20 03:04:09 amanet postfix/smtpd[111149]: connect from unknown[23.94.82.19]
Mar 20 03:04:09 amanet postfix/smtpd[111149]: warning: hostname 23-94-82-19-host.colocrossing.com does not resolve to address 23.94.82.19: No address associated with hostname
Mar 20 03:04:08 amanet postfix/smtpd[111147]: disconnect from unknown[23.94.82.19] ehlo=1 auth=0/1 commands=1/2
Mar 20 03:04:08 amanet postfix/smtpd[111147]: lost connection after AUTH from unknown[23.94.82.19]
Mar 20 03:04:08 amanet postfix/smtpd[111147]: warning: unknown[23.94.82.19]: SASL LOGIN authentication failed: authentication failure
Mar 20 03:04:07 amanet postfix/smtpd[112634]: disconnect from unknown[107.173.177.140] ehlo=2 starttls=1 auth=0/1 commands=3/4
Mar 20 03:04:07 amanet postfix/smtpd[112634]: lost connection after AUTH from unknown[107.173.177.140]
Mar 20 03:04:07 amanet postfix/smtpd[112634]: warning: unknown[107.173.177.140]: SASL LOGIN authentication failed: authentication failure
Mar 20 03:04:06 amanet postfix/smtpd[115524]: disconnect from unknown[183.236.9.133] commands=0/0
Mar 20 03:04:06 amanet postfix/smtpd[115524]: lost connection after CONNECT from unknown[183.236.9.133]
Mar 20 03:04:06 amanet postfix/smtpd[115524]: warning: connect to Milter service local:/var/run/milter-greylist/milter-greylist.sock: No such file or directory
Mar 20 03:04:06 amanet postfix/smtpd[115524]: connect from unknown[183.236.9.133]
Mar 20 03:04:05 amanet postfix/smtpd[111147]: warning: connect to Milter service local:/var/run/milter-greylist/milter-greylist.sock: No such file or directory
Mar 20 03:04:05 amanet postfix/smtpd[111147]: connect from unknown[23.94.82.19]
Mar 20 03:04:05 amanet postfix/smtpd[111147]: warning: hostname 23-94-82-19-host.colocrossing.com does not resolve to address 23.94.82.19: No address associated with hostname
Mar 20 03:04:05 amanet postfix/smtpd[111149]: disconnect from unknown[23.94.82.19] ehlo=1 auth=0/1 commands=1/2
Mar 20 03:04:05 amanet postfix/smtpd[111149]: lost connection after AUTH from unknown[23.94.82.19]
Mar 20 03:04:05 amanet postfix/smtpd[111149]: warning: unknown[23.94.82.19]: SASL LOGIN authentication failed: authentication failure
Mar 20 03:04:03 amanet postfix/smtpd[115553]: warning: connect to Milter service local:/var/run/milter-greylist/milter-greylist.sock: No such file or directory
Mar 20 03:04:03 amanet postfix/smtpd[115553]: connect from unknown[196.191.150.228]
Mar 20 03:04:03 amanet postfix/smtpd[111149]: warning: connect to Milter service local:/var/run/milter-greylist/milter-greylist.sock: No such file or directory
Mar 20 03:04:02 amanet postfix/smtpd[111149]: connect from unknown[23.94.82.19]
Mar 20 03:04:02 amanet postfix/smtpd[111149]: warning: hostname 23-94-82-19-host.colocrossing.com does not resolve to address 23.94.82.19: No address associated with hostname
Mar 20 03:04:01 amanet postfix/smtpd[112634]: warning: connect to Milter service local:/var/run/milter-greylist/milter-greylist.sock: No such file or directory
Mar 20 03:04:01 amanet postfix/smtpd[112634]: connect from unknown[107.173.177.140]
Mar 20 03:04:01 amanet postfix/smtpd[112634]: warning: hostname 107-173-177-140-host.colocrossing.com does not resolve to address 107.173.177.140: No address associated with hostname
Mar 20 03:04:01 amanet postfix/smtpd[112530]: disconnect from unknown[107.173.177.140] ehlo=2 starttls=1 auth=0/1 commands=3/4
Mar 20 03:04:01 amanet postfix/smtpd[112530]: lost connection after AUTH from unknown[107.173.177.140]
Mar 20 03:04:01 amanet postfix/smtpd[112530]: warning: unknown[107.173.177.140]: SASL LOGIN authentication failed: authentication failure
Mar 20 03:03:57 amanet postfix/smtpd[115745]: disconnect from unknown[192.210.236.155] ehlo=2 starttls=1 auth=0/1 commands=3/4