Delete a users messages across my entire server.

[vital karma]

Not really no. There's no way to bulk delete past 14 days or to search messages by user

Your best bet is simply a ban deleting back 7 days

Even if that werent API spam, you would still need to ability to fetch by user, which you dont

You cannot fetch messages by author

At all

Anywhere

They probably do a general fetch per channel, filter by user locally, the bulk delete