I can only receive emails, but I can't send emails.

aaP_nnhat2796

LOG:
2024-09-05T16:59:10.255425+00:00 mail postfix/smtp[3712]: connect to gmail-smtp-in.l.google.com[74.125.68.27]:25: Connection timed out
2024-09-05T16:59:10.255865+00:00 mail postfix/smtp[3712]: connect to gmail-smtp-in.l.google.com[2404:6800:4003:c00::1b]:25: Network is unreachable
2024-09-05T16:59:10.255992+00:00 mail postfix/smtp[3712]: connect to alt1.gmail-smtp-in.l.google.com[2607:f8b0:400e:c00::1a]:25: Network is unreachable
2024-09-05T16:59:14.267460+00:00 mail dovecot: imap-login: Login: user=admin@kiemtienchill.net, method=PLAIN, rip=::1, lip=::1, mpid=3757, secured, session=<0QraNWIhjogAAAAAAAAAAAAAAAAAAAAB>
2024-09-05T16:59:14.277647+00:00 mail dovecot: imap(admin@kiemtienchill.net)<3757><0QraNWIhjogAAAAAAAAAAAAAAAAAAAAB>: Disconnected: Logged out in=32 out=560 deleted=0 expunged=0 trashed=0 hdr_count=0 hdr_bytes=0 body_count=0 body_bytes=0
2024-09-05T16:59:14.421679+00:00 mail dovecot: imap-login: Login: user=admin@kiemtienchill.net, method=PLAIN, rip=::1, lip=::1, mpid=3759, secured, session=<N2/cNWIhnIgAAAAAAAAAAAAAAAAAAAAB>
2024-09-05T16:59:14.442708+00:00 mail dovecot: imap(admin@kiemtienchill.net)<3759><N2/cNWIhnIgAAAAAAAAAAAAAAAAAAAAB>: Disconnected: Logged out in=44 out=662 deleted=0 expunged=0 trashed=0 hdr_count=0 hdr_bytes=0 body_count=0 body_bytes=0
2024-09-05T16:59:15.544349+00:00 mail dovecot: pop3-login: Disconnected: Inactivity (no auth attempts in 180 secs): user=<>, rip=178.176.80.33, lip=128.199.129.173, session=<C6rtNWIhKOCysFAh>
2024-09-05T16:59:16.507720+00:00 mail postfix/smtpd[3706]: connect from localhost[::1]
2024-09-05T16:59:16.510900+00:00 mail postfix/smtpd[3706]: 7CAEC108932: client=localhost[::1], sasl_method=LOGIN, sasl_username=admin@kiemtienchill.net
2024-09-05T16:59:16.553692+00:00 mail postfix/cleanup[3710]: 7CAEC108932: message-id=0215641e0710e7020fe8670e96a0349e@kiemtienchill.net
2024-09-05T16:59:19.436532+00:00 mail postfix/qmgr[3327]: 7CAEC108932: from=admin@kiemtienchill.net, size=590, nrcpt=1 (queue active)
2024-09-05T16:59:19.436847+00:00 mail postfix/smtpd[3706]: disconnect from localhost[::1] ehlo=1 auth=1 mail=1 rcpt=1 data=1 quit=1 commands=6
2024-09-05T16:59:19.456588+00:00 mail postfix/smtp[3761]: connect to gmail-smtp-in.l.google.com[2404:6800:4003:c00::1b]:25: Network is unreachable
2024-09-05T16:59:19.457560+00:00 mail dovecot: imap-login: Login: user=admin@kiemtienchill.net, method=PLAIN, rip=::1, lip=::1, mpid=3763, secured, session=<UUcpNmIhkOAAAAAAAAAAAAAAAAAAAAAB>
2024-09-05T16:59:19.480230+00:00 mail dovecot: imap(admin@kiemtienchill.net)<3763><UUcpNmIhkOAAAAAAAAAAAAAAAAAAAAAB>: Disconnected: Logged out in=450 out=729 deleted=0 expunged=0 trashed=0 hdr_count=0 hdr_bytes=0 body_count=0 body_bytes=0
2024-09-05T16:59:20.136472+00:00 mail dovecot: imap-login: Login: user=admin@kiemtienchill.net, method=PLAIN, rip=::1, lip=::1, mpid=3765, secured, session=<AagzNmIhnuAAAAAAAAAAAAAAAAAAAAAB>
2024-09-05T16:59:20.159796+00:00 mail dovecot: imap(admin@kiemtienchill.net)<3765><AagzNmIhnuAAAAAAAAAAAAAAAAAAAAAB>: Disconnected: Logged out in=44 out=662 deleted=0 expunged=0 trashed=0 hdr_count=0 hdr_bytes=0 body_count=0 body_bytes=0
2024-09-05T16:59:20.316988+00:00 mail dovecot: imap-login: Login: user=admin@kiemtienchill.net, method=PLAIN, rip=::1, lip=::1, mpid=3769, secured, session=<mmQ2NmIhoOAAAAAAAAAAAAAAAAAAAAAB>
2024-09-05T16:59:20.325528+00:00 mail dovecot: imap-login: Login: user=admin@kiemtienchill.net, method=PLAIN, rip=::1, lip=::1, mpid=3770, secured, session=<j4k2NmIhpOAAAAAAAAAAAAAAAAAAAAAB>
2024-09-05T16:59:20.332157+00:00 mail dovecot: imap(admin@kiemtienchill.net)<3770><j4k2NmIhpOAAAAAAAAAAAAAAAAAAAAAB>: Disconnected: Logged out in=119 out=835 deleted=0 expunged=0 trashed=0 hdr_count=0 hdr_bytes=0 body_count=0 body_bytes=0
2024-09-05T16:59:20.354715+00:00 mail dovecot: imap(admin@kiemtienchill.net)<3769><mmQ2NmIhoOAAAAAAAAAAAAAAAAAAAAAB>: Disconnected: Logged out in=294 out=4365 deleted=0 expunged=0 trashed=0 hdr_count=8 hdr_bytes=1526 body_count=0 body_bytes=0
2024-09-05T16:59:21.497296+00:00 mail dovecot: pop3-login: Disconnected: Inactivity (no auth attempts in 180 secs): user=<>, rip=178.176.80.33, lip=128.199.129.173, session=<fH5INmIhXzSysFAh>

When I run the command below to check, it shows the result as in the image:
openssl s_client -connect mail.kiemtienchill.net:587 -starttls smtp
I’ve tried removing and reinstalling SSL multiple times, but it still doesn’t work.

aaP_demo1

aaP_nnhat2796

Does your server opened port 25? possible, if your server provider open it for you if they disallow for some reason.
If the port 25 is allow, try:
telnet gmail-smtp-in.l.google.com 25
or
telnet alt1.gmail-smtp-in.l.google.com 25

The SSL Certificate issue on mail server that you currently have, you should remove/delete the certificate and reissue it once again. After the reissue successfully, please do not click Save button; just click on X button to leave.
Then check on your SSL Certificate on your mail server again by
openssl s_client -connect mail.yourdomain.tld:587 -starttls smtp

aaPanel_Kern

aaP_nnhat2796
At the same time, check the postfix configuration, which can be viewed in the server status
"mail.135mailtest.com" is replaced with your domain name
Put:
smtpd_tls_chain_files=/etc/ssl/private/ssl-cert-snakeoil.key,/etc/ssl/certs/ssl-cert-snakeoil.pem
Change to:
smtpd_tls_chain_files = /www/server/panel/plugin/mail_sys/cert/135mailtest.com/privkey.pem,/www/server/panel/plugin/mail_sys/cert/135mailtest.com/fullchain.pem
Note to replace 135mailtest.com with your domain name.
Also check /www/server/panel/plugin/mail_sys/cert/135mailtest.com/ for privkey.pem and fullchain.pem files

You can use this command to check whether the correct SSL is configured
openssl s_client -connect mail.135mailtest.com:587 -starttls smtp
or
openssl s_client -connect mail.135mailtest.com:465 -starttls smtp

If the display is not OK, try to save the SSL certificate again, or please re-apply for SSL

Unable to send dkim headers
Troubleshoot log /var/log/rspamd/rspamd.log
Prompt for permission issues:
2022-04-20 00:27:56 #1363(rspamd_proxy) <6795e9>; proxy; dkim_module_load_key_format: cannot load dkim key /www/server/dkim/xx.com/default.private: cannot map key file: '/www /server/dkim/xx.com/default.private' Permission denied

Set 640 to 644, then restart rspamd to send emails to view the email source code, please replace xxx.com with your domain name.

chmod 644 /www/server/dkim/xx.com/default.private systemctl restart rspamd

Use this website to check whether the records of DKIM and SPF are correct?
https://www.dmarcanalyzer.com/dkim/dkim-checker/
https://dnschecker.org/spf-record-validation.php

Check the mail score and troubleshoot according to its error message
https://www.mail-tester.com/

Check blacklists
https://mxtoolbox.com/

Sending to gmail needs to configure SSL, do DKIM, SPF, it is best to let the network provider make the PTR RDNS record of ip