Added your custom headers to mailnews.customHeaders and I see the parse error. If I remove just the last one (the email address) icloud remains happy and I see the sent messages in Inbox and Send Messages
Bug 1846109 Comment 18 Edit History
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Added your custom headers to mailnews.customHeaders and I see the parse error. If I remove just the last one (the email address) icloud remains happy and I see the sent messages in Inbox and Sent Messages