Re: bug: 1581553 (duplicate) The mail.server.default.mime_parts_on_demand=false workaround works on my Windows 10 system. In my case the bug only occurred with one message (with a PDF attachment) in one account. If I copied the message to other IMAP accounts (including another one by the same email provider) it had no problem. There were also other messages with PDF attachments that were unaffected.
Bug 1576584 Comment 32 Edit History
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Re: bug 1581553 (duplicate) The mail.server.default.mime_parts_on_demand=false workaround works on my Windows 10 system. In my case the bug only occurred with one message (with a PDF attachment) in one account. If I copied the message to other IMAP accounts (including another one by the same email provider) it had no problem. There were also other messages with PDF attachments that were unaffected.