Recently, possibly when version was changed to 110, my message centre stopped clearing itself with every save/load cycle. While this can be useful, I can't find a way to clear out an ever increasing amount of useless messages. I now have almost five years of messages lying around in the message centre and the drag box in the scroll bar has become so small it's pretty much useless even if I manage to click it. I fear how it will be after 100 game years.
There will be at most 2000 messages saved. YOu can used the tabs to select just the categories you need.
Nice to know that it won't grow forever. I never use the tabs as I'm usually interested in everything except speed records and 95 % of the station crowded messages (the remaining 5 % are however critical).