Ok, in Admin I configured four pop accounts, assigned them to my local user.
Logged in with that user in Horde, and added one of above accounts in the Mail tab. (Don't ask why, it was possible so I did it. Better twice and one works than none.)
Started retrieving mails. Got lots of triples. Next time I log on I get 1600 new emails, page upon page with duplicated message.
Next time 2500 something emails.
Now I daren't log on anymore.
How to delete and fix this?
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Horde has gone berserk!
Is it Horde or Fetchmail
Horde may only be showing you what fetchmail is doing. First separate the problem.
1+1=2
If you collect from pop3 by fetchmail and horde i think you created this yourself
"Don't ask why, it was possible so I did it. Better twice and one works than none." No need to collect content from same server twice. When you want to be safe then collect your email locally from your imap with settings "save locally" then you know for sure your email is on more than one disk eventually 
Good luck
If you collect from pop3 by fetchmail and horde i think you created this yourself


Good luck