Is there a way that when you are out of office on annual leave for example and a client @mentions you/replies to a comment through the portal they can see your OOO response and know that they will not be responded to until you return? You can put an OOO on your emails but this is not reflected with the commenting section.
The only thing I have been advised of is @mentioing a colleague in any work or comments before going on leave so they see the reply but this is not an ideal solution.