Official way to monitor servers. Cons: Only works if the bot was active before deletion. BetterDiscord Plugins
While server admins can see who deleted a message in the Audit Log, the actual content of the deleted message is not recorded.
Can see both deleted and edited messages. Cons: Violates Discord's Terms of Service and can lead to account bans. Data Scraping Tools
Bots like Dyno or MEE6 can be configured to log message events to a private moderator channel.
If you need to ensure messages are preserved for evidence or archival:
When a user or moderator deletes a message, it is purged from Discord's active databases.