At the moment, I cannot upload any file to the Hubspot FTP server. The server always replies with a 551 reply code, which, according to http://www.serv-u.com/kb/1534/551-FTP-Reply-Code, means the following:
A 551 reply code may be sent in response to any command requiring the server to store information locally. It is a permanent negative reply, which means the client is discouraged from sending the command again since the server will respond with the same reply code. It is only applicable when the page file structure is being used (through a “STRU P” command).
I am using FTP since decades and didn’t even know that something like a “file structure” even existed. According to the STRU command description, the file structure can be “page”, “record”, or “file”, with the latter being supposed to be the default.
I am using FileZilla for the upload, which has worked successfully before. According to the FilleZilla log, it does not send the STRU command, so I would say the error is on the server side; perhaps it maintains a wrong default.
(One day I’d like to discuss the question why Hubspot uses such an outdated tool like FTP for file upload and does not support something much more usable like rsync. However, that’s a totally different question – though a very valid and important one! Customer satisfaction, you know!)