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Error 503: Unable to connect to a secure FTP in Marketing Cloud

Knowledge Article Number 000213705
The Enhanced FTP is used as a storage area to manage files moving in and out of the Marketing Cloud.  You may need to connect to it to upload a file that's to be imported to a List or Data Extension, or to retrieve files that have been uploaded to the FTP from the Marketing Cloud.  

The 503 error appears when there's an incorrect port number in the Port field of your third-party FTP client, or if "sftp://" is missing from the beginning of the address string entered into the Host field when it's used with a secure FTP site. 

Here's the full error message you'll see: 


"Response: 503 Invalid sequence of commands (AUTH SSL/TLS required prior to authentication).

Error: Could not connect to server"


Add "sftp://" to the Host field address

1. Find the Host address field in your third-party FTP client.
2. Add "s" to the beginning of the ftp:// portion of the address, so that it reads "sftp://."

Enter the port number into the Port field

If you're connecting to a standard FTP site, leave the Port field blank.  If you're connecting to an SFTP site:

1. Find the Port Number field in your third-party FTP site.
2. Enter 22.

Note: Marketing Cloud doesn't offer a client to access your Enhanced FTP site directly. It's recommended to contact your internal System Administrator to advise which third-party FTP clients are available for your use.

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