Why is DigitalOcean blocking outbound port 25 on my Droplet?

Hello DigitalOcean Support Team,

I’m experiencing an issue where outbound SMTP on port 25 from my Droplet (IP 164.92.85.163) is not working. I’ve spent considerable time troubleshooting and here are the steps I’ve taken so far:

1. Verified Exim was running

   • Confirmed Exim daemon is active and listening on port 25.

   • Sent local tests (mail -s “Test” root@localhost) which succeeded.

2. Flushed and opened local queues

   • Cleared the Exim spool (systemctl stop exim; rm -rf /var/spool/exim/input/* /var/spool/exim/msglog/*; systemctl start exim).

   • Ensured no messages remain in the queue (exim -bpc returned 0).

3. Checked DNS/MX configuration

   • Verified correct MX records for my domain (dig MX speedyturtleonline.com +short returns valid MX).

   • Added my domain to /etc/remotedomains so Exim treats it as remote.

4. Disabled all local firewalls

   • Confirmed ufw was inactive, csf was reloaded with port 25 allowed, and nft rules include permit for tcp dport 25 ct state new.

   • Ran csf -r to flush and rebuild iptables chains.

5. Confirmed local packet flow

   • Used tcpdump -nn -i any 'tcp port 25 and (tcp[tcpflags] & (tcp-syn|tcp-ack) != 0)'.

   • Observed outgoing SYNs to external mail servers (e.g. 74.125.137.27:25), but no SYN-ACK replies ever arrive.

6. Port scan & connectivity tests

   • Installed netcat-traditional and ran nc -vz gmail-smtp-in.l.google.com 25, which hung indefinitely.

   • Verified with tcpdump that SYNs go out but never return.

   • Confirmed DNS resolution and routing are correct.

These results strongly indicate that outbound TCP port 25 is being blocked upstream of my Droplet, as no external mail server is responding. Could you please remove any port-25 egress restrictions on this Droplet so that it can deliver mail directly to MX hosts?

Thank you for your assistance. If you need any further details or logs, please let me know.