Messaging filters are available to members in order to avoid being contacted by certain statuses (single man, single woman, couple only, certified member only, my contacts or my membership only, age restriction, etc.) or by members who have been registered for less than 10 days for example.
You can set your filters from your account settings (top right of the classic version of the site), under "privacy" and "who can message me".
Web version :
Mobile version :