User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:42.0) Gecko/20100101 Firefox/42.0 Build ID: 20151029151421 Steps to reproduce: Receive email where subject line is iso-2022-jp encoded but the first character of the subject is an ascii character. Here is a snippet from the source of one such message: Subject: [SMBC$B?.Bw6d9T(J] $B%$%s%I3t$N>e>:4pD4$OB3$$$F$$$h$&(J - $B%W%l%9%F%#%"(J $B%$%s%5%$%H(J 2015/11/12 MIME-Version: 1.0 Content-Type: text/plain; format=flowed; charset="iso-2022-jp"; reply-type=original Content-Transfer-Encoding: 7bit Here is how it displays in the message window: [SMBC信託銀行] インド株の上昇基調は続いていよう - プレスティア インサイト 2015/11/12 Actual results: Subject line displays correctly when message is opened, but does not display correctly in mailbox (list view) of messages. Expected results: Should have worked correctly.

Please attach a sample as .eml.

Here is a .eml as requested

Thank you for the sample. The subject of the message header is invalid. It needs to be RCF 2047 encoded but it is not. It contains straight iso-2022-jp encoded text. This is invalid. Yes, you observed correctly that the subject is displayed in two different ways in the user interface. That is regrettable, but we already know about that, see bug 1146099. The display of message headers will be unified, so their display is always the same. In the case of this message, it would always look wrong.