You have the ability to manage a permanent MemoServ ignore list with this command. All nicknames added to your ignore list must be registered. If a nickname on your ignore list tries to send you a memo, the ignored person will be notified that they are on your ignore list and you do not wish to receive any memos from them.
/msg memoserv ignore add benny
/msg memoserv ignore del Dainera
/msg memoserv ignore list
This is a good way to avoid memos from people who spam you. They can get around an ignore by registering a different nickname, but if people do so just to continue spamming, you can report them to whomever is running the chat network. MemoServ abuse is uncommon since it requires that the person register a nick to do it, and thus leaves a record of who was causing problems.