Both may not be able to stop PM spam full stop but will definitely will make it harder for the pm system to be used for spam. Any other ideas of suggestions, please post them here.
Delete all PM's from existing spamming member:
DELETE ibf_message_topics.*, ibf_message_text.* FROM ibf_message_topics LEFT JOIN ibf_message_text ON ibf_message_topics.mt_msg_id=ibf_message_text.msg_id WHERE ibf_message_topics.mt_from_id=X
Full Source: https://www.invision...p...icle&id=380