To maintain the high reputation of our IP ranges and prevent spam blacklisting, we closely monitor outgoing TCP Port 25.
Standard Usage
Legitimate, transactional email sending is fully permitted. However, you must ensure your server is properly authenticated (SPF, DKIM, DMARC, and rDNS configured).
Automated Restrictions
If our network detects anomalous, high-volume outgoing spam or botnet-like behavior on Port 25, an automated safety block is applied to protect the network. If your server is compromised and sending spam, your Port 25 will be blocked until the malware is removed.
Best Practice
For client-to-server mail submissions, always use Port 587 (STARTTLS) or Port 465 (SSL/TLS) instead of plain Port 25.
