Is there a list of FTP servers SyncBackSE/Pro have been tested on?
Although SyncBack is designed to support all FTP servers, unfortunately not all FTP servers are the same, nor are they all bug free. When choosing an FTP server you should be aware of the following:
MDTM, MFMT, and SITE UTIME
The MDTM command has two functions: to get the last modification date & time of a file, and to set the last modification date & time of a file. Most servers support getting the date & time, but some do not support setting the date & time. SyncBack will also try to use the MFMT and SITE UTIME commands to set a files date & time. If the FTP server doesn't support any of those commands then SyncBack has two options: to change the local files date & time to match that of the file on the FTP server (the default), or to record the date & time of the local file in the Fast Backup results (you must enable Fast Backup and disable the option "Force the file modification date & time to be correct" on the Copy/Delete tab).
MLSD
This command is used to retrieve the details of all files and directories within a directory on the FTP server. If a server supports this command then SyncBack can scan the server considerably faster. If the server does not support this command then SyncBack must make two extra calls per file to the server. For example, if a server supports MLSD then only one call to the server is required per directory, but if it doesn't support MLSD then there will be one call to get the list of files and subdirectories, followed by two calls per file in that directory. SyncBackFree does not support MLSD.
MODE Z
A few servers support MODE Z compression. This allows files to be sent to and retrieved from the server in compressed format. For high bandwidth connections it's generally not necessary to use MODE Z compression. Also note that some servers may support MODE Z compression but the administrators of that server may have disabled it (as it uses more CPU time and so could overload the server). SyncBackFree does not support MODE Z.
SSL
Some servers support SSL/TLS encryption (implicit and/or explicit). If the server does support it then SyncBack can securely send and receive files to and from the server. Note that encryption does impact performance and so should only be used if required. SyncBackFree does not support SSL.
UTF
FTP is a text protocol, not binary. Therefore, it can have problems with some file names, e.g. Chinese. To get around this problem some FTP servers accept filenames in UTF-8. UTF-8 is an ASCII-preserving encoding method for Unicode (ISO 10646), the Universal Character Set (UCS). Please note that even though some FTP servers claim to support UTF-8, their implementation of it is either broken or partially working.
XCRC
If the server supports the XCRC extension, then SyncBack can verify that files transferred to or from the server have been transmitted correctly, i.e. the file on the FTP server is the same as the local file based on its CRC value.
SFTP
Only SyncBackPro supports SFTP servers. Note that SFTP servers do not use any of the features above as they have a completely different communications protocol.
You may also want to view the following article:
https://www.2brightsparks.com/resources/articles/essential-ftp-features.html