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Sohan ShirodkarSohan Shirodkar 

Thread_Id merge field not resolved in HTML email template

I have an HTML Email Template containing two merge fields at the end: 
[{!Case.Thread_Id}]

{!EmailMessage.TextBody}

When I reply to an email and select this email template, it resolves the thread id part properly.

But when the email is actually sent, the thread_id merge field is empty. Outlook shows the thread id right at the bottom of the email, oustide the email template body.

What am I doing wrong?

FYI, the plain text version of the template is copied over from HTML version. Thread_Id merge field not resolved in HTML email template
I have an HTML Email Template containing two merge fields at the end: