Allow a username blacklist.
If Twitch won't filter (or ban) usernames containing personal information, perhaps streamers could blacklist names containing certain words/#s/etc.

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ChuckG997 commented
Please add this feature. Our troll has bypassed the chat moderation feature by creating usernames to doxx, threaten and otherwise harass us. We've had to disable follow alerts all together
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JATMN commented
This would be great to have. I have seen users make alts of the streamers IRL name or streamer handle to harass them thru follow notifications etc. It would be nice to block these via blacklist wildcards
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Bagley_ commented
I second this. A streamer I mod for (and several others who stream the same game) has been relentlessly harassed by the same troll. He's been at it for nearly 2 years now, and has created well over 1000 alts (it's always the same username followed by a random string of numbers).