Common attacks and weaknesses
- Password spraying against mailboxes.
Port 993: IMAPS
IMAP over TLS.
993
How IMAPS works
EmailThe mail client connects to port 993 to download or sync the messages waiting in the mailbox. Everything is encrypted: someone on the path only sees unreadable bytes.
- Transport
- TCP
- Exposure risk
- 3/10 moderate if reachable from the Internet
- Encryption
- EncryptedTLS or built-in crypto
- IANA status
- Assigned1 registered service
- Range
- Well-known (0-1023)
- Category
Is port 993 dangerous?
How to secure it
- Rate-limit logins and require modern authentication.
IANA registry entries for port 993
| Service | Port | Transport | Description | Reference | Updated |
|---|---|---|---|---|---|
| imaps | 993 | TCP | IMAP over TLS protocol | RFC 3501, RFC 8314, RFC 9051 | 2021-02-22 |
| - | 993 | - | Reserved | - | - |
// source: IANA service name and port number registry
Which program uses port 993, and is it reachable?
Linux
sudo ss -ltnup 'sport = :993' # process listening on 993
sudo lsof -nP -i :993macOS
sudo lsof -nP -i :993
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 993 -State Listen | Select LocalAddress, OwningProcess Get-NetUDPEndpoint -LocalPort 993 netstat -ano | findstr :993
From another machine
nmap -p 993 -sV <host> nc -zv <host> 993
Block it in the firewall
sudo ufw deny 993/tcp # Linux (ufw) New-NetFirewallRule -DisplayName "Block 993" -Direction Inbound -LocalPort 993 -Protocol TCP -Action Block # Windows
What is port 993 used for?
IMAP over TLS.
Is port 993 TCP or UDP?
Port 993 is registered for TCP.
Is it safe to open port 993?
It is rated 3/10 (moderate) when exposed to the Internet. Password spraying against mailboxes. Rate-limit logins and require modern authentication.
How do I check if port 993 is open?
On Linux run "ss -ltnup 'sport = :993'", on macOS "lsof -nP -i :993", and on Windows "netstat -ano | findstr :993" to see the local process. From another machine, "nmap -p 993 <host>" shows whether it is reachable.