Windows 10 Pro 64-bit, Thunderbird 52.6.0. After working fine for months, suddenly (as of this morning), any E-mails that contain attachments show up as almost blank. Except for a single "dot" character. No "From", no "To", no "Subject", no content. Step 1: Disabled add-ons (didn't have any but whatever) & restarted in Safe Mode. Tried sending an E-mail with an attachment to myself, from a different e-mail account on a different device. Same issue. Step 2: Disabled antivirus. Tried sending a test E-mail again. Same issue. E-mails WITHOUT attachments show up perfectly fine. E-mails WITH attachments - any attachment, of any size, even a tiny 2KB JPEG - show up as a dot. The same E-mails do show up in the sender's "Sent" box, and are received by another copy of Thunderbird on another computer. So it's not an issue with the account/password, it's something with my specific Thunderbird instance. See red-outlined items in the attached screenshot. Any suggestions?