Sorry for the late reply; it's been...a week.
Here's one of my save files: https://drmccoy.de/zeugs/hardcoded_beryl_mail_bug-savefile0.json
Just load it, go to Beryl's apartment and the conversation that adds the mail will pop right up, even though the mail is already on the "read" list. Twice, even.
Still happens with 1.05 too, I just tried.