How to backup Email with Webmail Horde
Log into Webmail using Horde. Example: https://webmail.yourdomain.com
Warning: If you log into Roundcube webmail, you’ll need to click your email address in the upper corner, then Horde.
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or under cPanel Webmail select horde
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Right-click Inbox and click Export emails in Inbox, Drafts, Sent, and their subfolders.
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Choose to download a standard or Zip compressed MBOX file and click OK.
Save the file.