Port 587: Mail Submission
Mail clients sending through their server, with STARTTLS and authentication. The standard port for sending mail from a client; it is not blocked like port 25.
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Port 587 at a glance
Port587
ProtocolTCP
ServiceMail Submission
Open to the Internet?Yes, if you run this service publicly
See What Is Listeningss -lntup | grep ':587 '
Test From Outsidenc -zv your-server 587
Block with UFWufw deny 587/tcp
Block with nftablesnft add rule inet filter input tcp dport 587 drop
Mail Submission uses TCP port 587. Mail clients sending through their server, with STARTTLS and authentication.
The standard port for sending mail from a client; it is not blocked like port 25.
Open port 587 only on servers that run Mail Submission, and keep the software patched: public services are scanned within minutes of going online.
Other Ports
20 FTP Data21 FTP22 SSH23 Telnet25 SMTP53 DNS67 DHCP Server80 HTTP110 POP3123 NTP143 IMAP161 SNMP389 LDAP443 HTTPS445 SMB465 SMTPS514 Syslog587 Mail Submission853 DNS over TLS993 IMAPS995 POP3S1194 OpenVPN1433 Microsoft SQL Server1900 SSDP / UPnP2049 NFS2083 cPanel (SSL)2087 WHM (SSL)3306 MySQL / MariaDB3389 RDP3478 STUN / TURN5060 SIP5432 PostgreSQL5900 VNC6379 Redis8006 Proxmox VE8080 HTTP Alternate8443 HTTPS Alternate11211 Memcached25565 Minecraft27017 MongoDB51820 WireGuard
Questions
What is port 587 used for?
Mail Submission. Mail clients sending through their server, with STARTTLS and authentication.
Is it safe to open port 587?
Yes, if you run this service publicly. The standard port for sending mail from a client; it is not blocked like port 25.
How do I check if port 587 is open?
On the server, ss -lntup | grep ':587 ' shows what is listening. From another machine, nc -zv your-server 587 shows whether the firewall lets it through.
How do I block port 587?
With UFW: ufw deny 587/tcp. With nftables, add a drop rule for dport 587 in your input chain.
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