The default limit for objects is 256 items, but the zl object (at least) can do up to 32767. Look at the "list length" tab in the zl help file. Also, other data types (jitter matrices) can hold more items and third party objects don't necessarily have these limits.
Using zl len I get 256 as the length. However, the mapping is performed and the output message box seems to contain all values. What would be an alternative external to use a bigger list? I think the maximum number of items I will use would be 10000 but I think I can limit it to 4096 if there would not be any alternative. In either case, I should be able to handle more than 256 values at a time.
@thinksamuel (even if late) : the zlmaxsize is the maximum size of a list that can be processed. The length given by zl length is the actual size of the list. Therefore, zlmaxsize will always be superior or equal to a list length.