Cannot send emails, is Port 25 blocked ?

I am not able to send mail using a newly setup Linode. I am using the current version of virtualmin 6.08 gpl on ubuntu 18.04 LTS. The mail.log is as follows …

Apr 28 18:28:40 nextechnetwork postfix/smtpd[12750]: disconnect from battery.census.shodan.io[93.174.95.106] commands=0/0
Apr 28 18:32:00 nextechnetwork postfix/anvil[12749]: statistics: max connection rate 10/60s for (smtp:93.174.95.106) at Apr 28 18:28:36
Apr 28 18:32:00 nextechnetwork postfix/anvil[12749]: statistics: max connection count 2 for (smtp:93.174.95.106) at Apr 28 18:28:29
Apr 28 18:32:00 nextechnetwork postfix/anvil[12749]: statistics: max cache size 1 at Apr 28 18:28:25
Apr 28 18:41:49 nextechnetwork dovecot: pop3-login: Aborted login (auth failed, 1 attempts in 5 secs): user=info@nextechnetwork.com, method=PLAIN, rip=94.102.52.44, lip=172.105.48.225, session=<kxbcklmkzkxezjqs>
Apr 28 19:21:55 nextechnetwork postfix/qmgr[1277]: 6A73B9F0EE: from=nextechnetwork@nextechnetwork.com, size=648, nrcpt=1 (queue active)
Apr 28 19:21:55 nextechnetwork postfix/qmgr[1277]: D4AFD9F0F4: from=nextechnetwork@nextechnetwork.com, size=809, nrcpt=1 (queue active)
Apr 28 19:22:25 nextechnetwork postfix/smtp[18987]: connect to gmail-smtp-in.l.google.com[2404:6800:4003:c04::1a]:25: Connection timed out
Apr 28 19:22:25 nextechnetwork postfix/smtp[18988]: connect to gmail-smtp-in.l.google.com[2404:6800:4003:c04::1a]:25: Connection timed out
Apr 28 19:22:55 nextechnetwork postfix/smtp[18987]: connect to gmail-smtp-in.l.google.com[74.125.24.27]:25: Connection timed out
Apr 28 19:22:55 nextechnetwork postfix/smtp[18988]: connect to gmail-smtp-in.l.google.com[74.125.24.27]:25: Connection timed out
Apr 28 19:23:25 nextechnetwork postfix/smtp[18987]: connect to alt1.gmail-smtp-in.l.google.com[74.125.28.27]:25: Connection timed out
Apr 28 19:23:25 nextechnetwork postfix/smtp[18988]: connect to alt1.gmail-smtp-in.l.google.com[2607:f8b0:400e:c04::1b]:25: Connection timed out
Apr 28 19:23:55 nextechnetwork postfix/smtp[18988]: connect to alt1.gmail-smtp-in.l.google.com[74.125.28.27]:25: Connection timed out
Apr 28 19:23:55 nextechnetwork postfix/smtp[18987]: connect to alt1.gmail-smtp-in.l.google.com[2607:f8b0:400e:c04::1b]:25: Connection timed out
Apr 28 19:24:25 nextechnetwork postfix/smtp[18987]: connect to alt2.gmail-smtp-in.l.google.com[2607:f8b0:4003:c13::1b]:25: Connection timed out
Apr 28 19:24:25 nextechnetwork postfix/smtp[18988]: connect to alt2.gmail-smtp-in.l.google.com[2607:f8b0:4003:c13::1b]:25: Connection timed out
Apr 28 19:24:25 nextechnetwork postfix/smtp[18987]: 6A73B9F0EE: to=saurabh261187@gmail.com, relay=none, delay=82637, delays=82487/0.01/150/0, dsn=4.4.1, status=deferred (connect to alt2.gmail-smtp-in.l.google.com[2607:f8b0:4003:c13::1b]:25: Connection timed out)
Apr 28 19:24:25 nextechnetwork postfix/smtp[18988]: D4AFD9F0F4: to=saurabh261187@gmail.com, relay=none, delay=82540, delays=82390/0.01/150/0, dsn=4.4.1, status=deferred (connect to alt2.gmail-smtp-in.l.google.com[2607:f8b0:4003:c13::1b]:25: Connection timed out)</kxbcklmkzkxezjqs>

Can anyone please help with advising how to sort this out and whats wrong ? Also, I can send mail to internal users. Only externail mail is not working. Like if i want to send to gmail, etc.

Upon asking at Virtualmin forums I got the following reply : It looks like your ISP (Linode?) doesn’t allow traffic to port 25 directly from your IP address, or you have blocked port 25 outbound from your server in your firewall.

Kindly help.