Why Sophos UTM not sending emails out

Question

Hello Guys. Few days ago I had an issue with my internet resulted in changing my static IP. No since I've received a new IP I've updated my external DNS. 
 However since my IP has changed I no longer able to send out emails from my UTM. I have mailenable which is relaying to UTM. From logs I can see UTM accepts relaying from my mailenable server but emails get spooled and see this in the logs: 
 
 2019:02:28-22:14:00 sukafun-utm smtpd[5343]: MASTER[5343]: Action: Forcing delivery process for 1gzMQI-000BCR-0t 
 2019:02:28-22:15:00 sukafun-utm exim-out[43216]: 2019-02-28 22:15:00 Start queue run: pid=43216 
 2019:02:28-22:16:19 sukafun-utm exim-out[41492]: 2019-02-28 22:16:19 1gzJxs-0007Mg-Dl SSL_write: (from [192.168.7.77]:999) syscall: Connection timed out 
 2019:02:28-22:16:19 sukafun-utm exim-out[41492]: 2019-02-28 22:16:19 1gzJxs-0007Mg-Dl SSL_write error 5 
 2019:02:28-22:16:19 sukafun-utm exim-out[41492]: 2019-02-28 22:16:19 1gzJxs-0007Mg-Dl SMTP timeout while connected to mail-tester.com [94.23.206.89] after sending data block (25910 bytes written): Connection timed out 
 2019:02:28-22:16:19 sukafun-utm exim-out[41491]: 2019-02-28 22:16:19 1gzJxs-0007Mg-Dl == test-3tjbp@mail-tester.com R=dnslookup T=remote_smtp defer (110): Connection timed out: SMTP timeout while connected to mail-tester.com [94.23.206.89] after sending data block (25910 bytes written) 
 2019:02:28-22:16:20 sukafun-utm exim-out[43418]: 2019-02-28 22:16:20 1gzKXM-0008JN-HK == test-37cxi@mail-tester.com R=dnslookup T=remote_smtp defer (-53): retry time not reached for any host 
 2019:02:28-22:16:20 sukafun-utm exim-out[43422]: 2019-02-28 22:16:20 1gzKP8-00083Z-Gr == test-37cxi@mail-tester.com R=dnslookup T=remote_smtp defer (-53): retry time not reached for any host 
 2019:02:28-22:16:20 sukafun-utm exim-out[40075]: 2019-02-28 22:16:20 End queue run: pid=40075

It lets me send emails out to some domains like gmail but most of other domains not. I confirm that my ISP not blocking port 25. My UTM is connected to internet. My external DNS is correct. Tried enabling smarthost from UTM but same issue. What else should I look for? 
 I receive emails fine.

Cheers 
 Mo

DouglasFoster · Answer

I would assume that your ISP told you wrong. 
 
 Test DNS. Can you do an MX Lookup on example.com using UTM as your recursive dns server? Can you do a lookup on those mail server names and obtain an IP address. 
 Test with PING and TRACERT to see if you can get through the network to those devices. No guarantee that they respond to ping, but I expect most of them will. 
 Test SMTP Connectivity. Use the Microsoft Telnet client and try to "telnet mail.example.com 25". If you do not get any response, you are getting blocked. If you use Wireshark to monitor your test traffic, you may even see a reply packet that says "administratively blocked" 
 
 Of course, once you get connectivity solved, you have to get past the spam filters at the receiving end. Have you updated your MX record in DNS? Have you checked your domain and IP reputation using MXToolbox.com ?