993/TCPIMAPS
Email · Well-known port · OSI layer 7
IMAP over TLS: Read mail from your mailbox securely. Standard for email clients and smartphones.
IANA: officially registered as imaps
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Port 993: IMAPS for encrypted email retrieval
Port 993 (TCP) is used for IMAP with implicit TLS, also known as IMAPS. The tool shows you the details and generates firewall commands for your mail server.
Built by Justin Schuessler
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Ports
Firewall rule (inbound)
Firewall commands
Open port
sudo ufw allow 993/tcpNotes on ufw
For Ubuntu and Debian. ufw creates the rule for both IPv4 and IPv6. If ufw is disabled, allow SSH first (sudo ufw allow 22/tcp), then enable it with sudo ufw enable, or you'll lock yourself out.
On a ZAP-Hosting VPS with an active network firewall, you also need to allow the port in the Customer Panel.
Port 993 explained
What is port 993 used for?
Purpose
On port 993, email clients access a mailbox via IMAP over a connection encrypted with TLS from the start. This protects your username, password and emails in transit. It provides the same IMAP functionality as port 143: folders and read status are synchronized across all devices. Most email providers now list port 993 as the default for retrieving email.
Origin and standard
IANA lists port 993 as “imaps”, meaning IMAP over TLS. STARTTLS on port 143 was considered the preferred approach for a while, but port 993 remained widely used in practice. RFC 8314 from 2018 explicitly recommends implicit TLS for retrieving mail, and therefore port 993. The protocol itself is now described as IMAP4rev2 in RFC 9051.
Typical use
- Retrieving mail in Thunderbird, Outlook, or Apple Mail with the SSL/TLS setting
- Mail apps on smartphones connected through mobile networks
- Mail servers such as Dovecot that only offer encrypted connections
Security
Port 993 is a secure choice for IMAP as long as the certificate is valid and old TLS versions are disabled. Because the port must be accessible from the internet, it is a common target for password attacks. Protect authentication with strong passwords and tools such as Fail2ban. If all clients use port 993, you can close port 143 entirely.
More ports
Related ports
These ports are often part of the same setup. Click one to see its explanation and firewall commands.
View all well-known ports and the complete IANA list
Port list source: IANA Service Name and Transport Protocol Port Number Registry, as of October 22, 2026. iana.org
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FAQ
Frequently asked questions
Quick answers about port 993.
Port 993 uses TCP only. You do not need to allow UDP for IMAPS.
Port 993 is encrypted with TLS from the start. Port 143 starts unencrypted and is only encrypted if STARTTLS is used. Port 993 is easier to operate securely and is recommended by RFC 8314.
With ufw, sudo ufw allow 993/tcp is enough. With firewalld, run sudo firewall-cmd --permanent --add-port=993/tcp followed by sudo firewall-cmd --reload. On Windows, use New-NetFirewallRule to create an inbound rule for TCP 993.
First, check that your email client is set to SSL/TLS, not STARTTLS. Then check that the server's firewall allows port 993 and that the certificate matches the hostname. A port checker will quickly show whether the port is reachable from outside.
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