When is FTP over port 21 secure?

Port 21 is the control port for the original and unsecure FTP protocol.   Credentials and payload are exchanged over the network unencrypted.

However file transfer over port 21 can be made secure with the newer FTPS protocol. FTPS or  FTP over SSL/TLS can enable encryption of both the Control and Data Connections.  Port 990 and 889 are defined for 'implicit' FTPS whereby both Control and Data are encrypted: port 990 for Control, 889 for Data.   If the client connects on port 990 the assumption is that SSL/TLS encryption will be performed i.e. the port number signifies security. 

However 'explicit' FTPS runs over port 21 (the port used by original and unsecure FTP protocol).  FTP clients who connect on port 21 and require encryption, must send AUTH SSL or AUTH TLS to the server. If the server complies it will take steps to complete an SSL/TLS handshake.   Selective use of encryption enables transfers to be secured according to need, with benefit of greater speed for unencrypted exchanges.

DKIM, SPF, and DMARC Email authentication

Sender Policy Framework (SPF).

Publishes a list of servers that are authorised to send email on behalf of a domain. SPF is akin to path based authentication.

 

Domain Keys Identified Mail (DKIM).

A tamper proof domain seal to an email. DKIM is akin to signature based authentication.

 

Domain-based Message Authentication, Reporting and Conformance (DMARC).

Creates a link between a domain and an email, and validates SPF and DKIM authenticated headers match the from header domain.   DMARC builds upon SPF and DKIM authentication. Anyone can buy a domain and put SPF and DKIM in place. However DMARC closes off this problem by checking the SPF and DKIM authenticated headers ALSO match the domain found in the from header.  This is termed 'Identifier Alignment'.

 

Once an email domain owner is confident that they’ve deployed SPF and DKIM across all of their email streams, the domain owner can then tell the world to act against email that is not compliant with DMARC.  Not just gentlemanly but ensures brand protection and effective email delivery (by helping to prevent SPAM filter false positives).

 

DMARC is a freely available technical specification. DMARC records are published with DNS Domain.

 

Examples of DMARC Matching

From: rich.com   SPF: rich.com             DKIM: (none)               DMARC Match?  Yes

From: rich.com   SPF: paul.rich.com    DKIM: (none)               DMARC Match?  Yes

From: rich.com   SPF: richierich.com   DKIM: (none)               DMARC Match?  No

From: rich.com   SPF: richierich.com   DKIM: rich.com           DMARC Match?  Yes

From: rich.com   SPF: paul.rich.com    DKIM: paul.rich.com   DMARC Match?  Yes

From: rich.com   SPF: tealeaf.com       DKIM: crook.com        DMARC Match?:  No

From: rich.com   SPF: r1ch.com            DKIM: (none)               DMARC Match?:  No