tmas_oestore.dll is a TMAS_OEStore
belonging to Trend Micro Anti-Spam
from Trend Micro Inc.
Non-system processes like tmas_oestore.dll originate from software you installed on your system. Since most applications store data in your system's registry, it is likely that your registry has suffered fragmentation and accumulated invalid entries which can affect your PC's performance. It is recommended that you check your registry to identify slowdown issues.