For individual DMs, take screenshots of important conversations as they occur.
While server admins can see who deleted a message in the Audit Log, the actual content of the deleted message is not recorded.
Third-party client mods like MessageLoggerV3 save local copies of all incoming chat. recover-deleted-messages-on-discord
Can see both deleted and edited messages. Cons: Violates Discord's Terms of Service and can lead to account bans. Data Scraping Tools
If you need to ensure messages are preserved for evidence or archival: Can see both deleted and edited messages
Request your Discord data package every few months to maintain a local archive of your existing history. Requesting a Copy of your Data - Discord Support
Users can request a copy of their personal data via User Settings > Privacy & Safety . However, this typically only includes messages that currently exist; manually deleted messages are usually excluded from these archives. Methods for Viewing Deleted Messages Requesting a Copy of your Data - Discord
Sites claiming to "retrieve deleted history" often use these scripts to steal accounts .