Port 587SMTP Submission
Port 587 is primarily used for the submission of email messages over the Simple Mail Transfer Protocol (SMTP). It is designated for client-to-mail server communication, allowing authenticated users to send outgoing emails securely, typically requiring authentication and optional encryption. This port replaces legacy port 25 for authenticated message submission to improve security and adherence to email standards..
- transport
- tcp
- in transit
- cleartext
- assignment
- official
- risk
- 4/10
- lookups
- 9,776
single transport
payload readable on path
registered with iana
caution
rank 487 of 993 · top 49%
Technical Details
what runs on :587Overview:
Port 587 is the default port for email message submission using SMTP. It is designed to facilitate the sending of outgoing mail from client devices or applications to email servers prior to relaying or further delivery. Unlike port 25, which is mainly used for server-to-server transmission (SMTP relay), port 587 enforces authentication, making it more appropriate for sending emails from end-users.
Protocol Details:
Port 587 supports the SMTP protocol with extensions specified in RFC 6409, which defines message submission. It generally requires the use of the STARTTLS command to upgrade from an unencrypted to an encrypted connection, ensuring confidentiality and integrity during transmission. Clients must authenticate via mechanisms such as LOGIN, PLAIN, or newer methods to submit messages successfully.
Usage Scenarios:
This port is the recommended submission port for email clients (e.g., Outlook, Thunderbird, mobile email apps) when sending mail. Many ISPs and hosting providers enforce message submission on port 587 with STARTTLS to meet best practices and enhance security without obstructing legitimate email sending activities.
Security Information
exposure of :587risk 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
every listening transport is another surface to filter at the edge
security overview
Common Vulnerabilities:
- Misconfiguration: Accepting unauthenticated connections can allow abuse by spammers.
- Lack of Encryption: Without enforcing STARTTLS, message content and credentials can be intercepted.
- Brute Force Attacks: Attackers may attempt credential guessing to hijack accounts.
- Improper Authentication: Weak or outdated authentication mechanisms can be exploited.
Common Mitigations:
- Enforce STARTTLS: Mandate TLS encryption to protect data in transit.
- Require Strong Authentication: Use robust authentication methods (e.g., OAuth2, strong SASL mechanisms).
- Apply Access Controls: Limit failed login attempts to prevent brute force attacks.
- Monitor and Log Activity: Track abnormal submission patterns indicating abuse.
- Utilize SPF, DKIM, and DMARC: Enhance sender verification and reduce email spoofing.
- Regularly Update Software: Patch email servers to address emerging vulnerabilities.
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