[Mailman-Users] newbe question as a moderator

[Mahmood Naderan]

Hello
I am a moderator of a list which uses mailman. Problem is every time, someone send a message to the list, the message is held for moderator (me) approval and this is a boring task because we know our members and the list is for internal messages.

The message received by moderator contains

Your mail to '....' with the subject ..... Is being held until the list moderator can review it for approval. The reason it is being held: Post by non-member to a members-only list

I looked at the available options and searched the manual for an option to remove that. However I couldn't find that.
Can someone point me to the right direction?
Regards,
Mahmood