Hello Claire,
In IFS EE, this is the maximum number of rows we allow for output channels. The reason for this limit is performance. In IFS EE output channels, the export happens at the client end. So basically when you ask a large number of rows to be fetched to the client, all client-side processing needs to be done and then reformatted as specified in the output channel specification. So it gets considerably slow as the row count increases. Thus we highly discourage using output channels to export large volumes of data, this functionality was only designed to cater to ad hoc data export requirements.
If you are dealing with larger data volumes, the correct approach would be to use quick reports. SQL quick reports have built-in “Export to Excel” functionality, where the Excel is generated at the server side itself, giving much faster output.