Stale mail on alpaca: Exception('No uuid or doc',)

This mail can't get processed by leap-mx due to an Exception('No uuid or doc',):

May 24 09:58:05 alpaca leap-mx: [-] Processing new mail at '/var/mail/leap-mx/Maildir/new/1495607981.Vca01Ia07802fM714768.alpaca'
May 24 09:58:06 alpaca leap-mx: [HTTP11ClientProtocol,client] Still stalled email FilePath('/var/mail/leap-mx/Maildir/new/1495607981.Vca01Ia07802fM714768.alpaca') for the last 3:18:23.876722: Exception('No uuid or doc',)
May 24 10:28:05 alpaca leap-mx: [-] Processing new mail at '/var/mail/leap-mx/Maildir/new/1495607981.Vca01Ia07802fM714768.alpaca'
May 24 10:28:06 alpaca leap-mx: [HTTP11ClientProtocol,client] Still stalled email FilePath('/var/mail/leap-mx/Maildir/new/1495607981.Vca01Ia07802fM714768.alpaca') for the last 3:48:23.886591: Exception('No uuid or doc',)
May 24 10:53:13 alpaca leap-mx: [-] Processing new mail at '/var/mail/leap-mx/Maildir/new/1495607981.Vca01Ia07802fM714768.alpaca'
May 24 10:53:13 alpaca leap-mx: [HTTP11ClientProtocol,client] New stalled email FilePath('/var/mail/leap-mx/Maildir/new/1495607981.Vca01Ia07802fM714768.alpaca'): Exception('No uuid or doc',)

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