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Never use a system that allows anonimity at work, be it benevolent feedback. Ignore information by unidentified sender, regardless of their content. Resist the temptation to figure out who the sender is/are for that leads to false accusations. Pretend that nothing happened. Don’t let the author laugh at your emotions, deeds, and (futile) efforts. Archive all anonim communications for possible investigation later. Feel compassion for the colleague, who hides cowardly behind anonimity.