Port 366ODMR
On-Demand Mail Relay (ODMR) facilitates mail delivery by allowing remote servers to retrieve queued email messages as needed, rather than relying solely on traditional push-based SMTP delivery. This enables efficient mail forwarding in scenarios where recipient servers have intermittent connectivity or are located behind firewalls, enhancing email flexibility for ISPs and mobile users..
- transport
- tcp · udp
- in transit
- cleartext
- assignment
- official
- risk
- 4/10
- lookups
- 9,100
2 transports registered
payload readable on path
registered with iana
caution
rank 538 of 993 · top 54%
Technical Details
what runs on :366On-Demand Mail Relay (ODMR), sometimes referred to as ATRN SMTP, is defined under RFC 2645 and is designed to optimize message delivery particularly in scenarios where servers are dynamically connected, such as dial-up or mobile email servers. It modifies the traditional client-server SMTP model by allowing the receiving server to initiate the collection of its emails when it is online, effectively flipping the communication direction.
ODMR primarily works by having the client connect to the ODMR-enabled server, authenticate itself, and then request pending email messages using the ATRN command. This command enables the server to transfer messages in the same session without waiting for the sender to establish a separate SMTP connection, thereby enhancing efficiency and reducing connection delays.
This protocol is important for ISPs and email hosting providers supporting customers with intermittent connectivity. Its design helps manage mail queues reliably, reduces unnecessary network retries, and ensures that queued messages are batched and delivered promptly upon client request.
Security Information
exposure of :366risk score
4/ 10caution
worth attention. how exposed you are depends on configuration — don't leave it reachable from the internet without a reason.
email averages 3.9 across 42 ports — this one sits 0.1 above.
in transit
cleartext
credentials and payloads are readable by anyone on path
assignment
official
registered with iana for this service — scanners fingerprint it by number
reachable over
tcp · udp
udp is connectionless — source addresses are trivially spoofed and it is a reflection favourite
security overview
Common vulnerabilities with ODMR stem from insufficient authentication mechanisms and the risk of unauthorized relaying if the service is not properly locked down. Attackers may exploit misconfigured ODMR services to use them as open relays for spam or malicious mail distribution. Additionally, as ODMR typically operates without encryption, transmitted data is susceptible to interception and man-in-the-middle attacks.
Mitigation strategies include deploying strong authentication methods like SMTP AUTH, enabling strict access controls to prevent open relay abuse, and where possible, tunneling ODMR connections through encrypted channels such as TLS. Regular auditing of server configurations for relay restrictions and monitoring for abnormal activity are also essential preventive measures.
Related Ports
the 8 most looked-up other ports in email — 42 ports carry that label.
| port | service | risk | |||
|---|---|---|---|---|---|
| :143 | IMAP | TCPUDP | caution | 20.7k | |
| :995 | POP3S | TCPtls | caution | 18.8k | |
| :109 | POP2 | TCP | caution | 17.9k | |
| :2096 | cPanel SSL Webmail | TCPtls | Web Services | safe | 17.4k |
| :110 | POP3 | TCP | caution | 15.5k | |
| :993 | IMAPS | TCPtls | caution | 14.5k | |
| :1352 | Lotus Notes RPC | TCP | caution | 12.3k | |
| :24 | Private Mail | TCPUDP | caution | 11.7k |
risk mix of the 8 listed
- safe13%
- caution88%
3 of 8 encrypted