One of my clients previously used AOL.com email addresses for their business. We've migrated them to Hosted Exchange, and have agreed to forward their incoming email from their old accounts to their new accounts for a period of time. I'm using Thunderbird 52.1.1 and collecting their emails from the old accounts, then using a forwarding rule to automatically forward those messages to their new mail boxes. In the first few days, I'm having some complaints that PDFs are arriving in the new mail box (exchange) with corrupted attachments. After scouring the forums, I've made the following changes within config editor, with limited success. mail.imap.mime_parts_on_demand to false mail.server.default.parts_on_demand to false mail.server.default.fetch_by_chunks to false mail.file_attach_binary --> True mail.content_disposition_type --> 1 mail.inline_attachments --> False Even after having made these changes, some attachments are being corrupted when auto-forwarded. Most recently, even a .txt file didn't make the trip safely. Has anyone else seen this issue, or have any tips?