Can email other servers, but not my other CWP server

I'm having trouble sending and receive email between my CWP servers. In this diagram, we'll use 1 and 2 to signify different CWP servers, with different IPs, different domains, on different VMs. Server 1 has 2 users, 3 domains. Server 2 has 1 user, 1 domain.

1 user 1 -> 1 user 2 -> success
1 user 2 -> 1 user 1 -> success
1 any domain -> Gmail -> success
Gmail -> 1 any domain -> success
1 user 1 -> Work -> success
Work -> 1 user 1 -> success
1 any domain -> 2 -> Connection refused
2 -> 1 any domain -> Connection refused
2 -> Gmail -> success
Gmail -> 2 -> success
2 -> Work -> success
Work -> 2 -> success

Something else, my first user on server 1 has 2 domains, but only 1 domain can get DKIM, and it's not the primary domain that has DKIM.

I don't know where to start for troubleshooting, I'm relatively new servers and managing email.

Could you please advise of the following:

What 'errors' and/or 'messages' are being displayed in the logs?

What distro are you are you running CWP on?

Public or NAT?

Sorry for the long delay of response.

Server 1 is running AlmaLinux 8 migrated from CentOS 8 Stream. Server 2 is running AlmaLinux fresh install. Both servers are running on VMs and Proxmox as the host OS.

They each have their own public IP.

This comes up "(connect to (mailserver)[IP]:25: Connection timed out)" when looking at the mail queue under the root control panel.

And for /var/log/maillog

Aug 21 14:45:13 localhost cbpolicyd[1882]: module=Quotas, mode=update, host=::1, helo=mail domain, from=admin@domain.tld, to=stray@domain.tld, reason=quota_update, policy=7, quota=4, limit=5, track=Sender:@domain.tld, counter=MessageCount, quota=1.00/200 (0.5%)
Aug 21 14:45:13 localhost postfix/smtpd[2161]: 290054055980: client=localhost[::1], sasl_method=LOGIN, sasl_username=admin@domain.tld
Aug 21 14:45:13 localhost postfix/cleanup[2170]: 290054055980: message-id=
Aug 21 14:45:13 localhost opendkim[1156]: 290054055980: DKIM-Signature field added (s=default, d=domain.tld)
Aug 21 14:45:13 localhost postfix/qmgr[1190]: 290054055980: from=, size=599, nrcpt=1 (queue active)
Aug 21 14:45:13 localhost postfix/smtpd[2161]: disconnect from localhost[::1] ehlo=1 auth=1 mail=1 rcpt=1 data=1 quit=1 commands=6
Aug 21 14:45:43 localhost postfix/smtp[2172]: connect to mailserver[IP]:25: Connection timed out
Aug 21 14:45:43 localhost postfix/smtp[2172]: 290054055980: to=, relay=none, delay=31, delays=0.39/0.05/30/0, dsn=4.4.1, status=deferred (connect to mailserver[IP]:25: Connection timed out)

Yet, when sending successfully to Gmail:

Aug 21 14:51:39 localhost postfix/smtpd[3095]: connect from localhost[::1]
Aug 21 14:51:39 localhost cbpolicyd[1884]: module=Quotas, mode=update, host=::1, helo=mail domain, from=admin@domain.tld, to=[personal]@gmail.com, reason=quota_update, policy=7, quota=4, limit=5, track=Sender:@domain.tld, counter=MessageCount, quota=1.89/200 (0.9%)
Aug 21 14:51:39 localhost postfix/smtpd[3095]: 1914440A5367: client=localhost[::1], sasl_method=LOGIN, sasl_username=admin@domain.tld
Aug 21 14:51:39 localhost postfix/cleanup[3100]: 1914440A5367: message-id=
Aug 21 14:51:39 localhost opendkim[1156]: 1914440A5367: DKIM-Signature field added (s=default, d=domain.tld)
Aug 21 14:51:39 localhost postfix/qmgr[1190]: 1914440A5367: from=, size=581, nrcpt=1 (queue active)
Aug 21 14:51:39 localhost postfix/smtpd[3095]: disconnect from localhost[::1] ehlo=1 auth=1 mail=1 rcpt=1 data=1 quit=1 commands=6
Aug 21 14:51:39 localhost postfix/smtp[3101]: 1914440A5367: to=, relay=gmail-smtp-in.l.google.com[142.251.116.26]:25, delay=0.76, delays=0.15/0.02/0.18/0.41, dsn=2.0.0, status=sent (250 2.0.0 OK 1724269899 5614622812f47-3dd33da3471si6199819b6e.195 - gsmtp)
Aug 21 14:51:39 localhost postfix/qmgr[1190]: 1914440A5367: removed