No, that's incorrect. The FTP server does not reject files over 3MB. In fact, FTP connection is persistent, so if you upload a very large file, the data is continuously sent to the FTP server. The FTP server does not reject it.
Dependent on your connection speed, when you upload a very large file, it could appear as if the network is idle. This is because FTP protocol requires two connections (channels): the Command Connection and the Data Connection. While the data connection is busy transferring data, the command connection is idle waiting for the data connection to finish. Under certain network circumstances, this could cause the command connection to time out.
Therefore, it is always recommended using a more sophisticated FTP client, such as FileZilla to upload very large files. DriveHQ FileManager is the best option as it is seamlessly integrated with our service.