I am manually creating a multi-part MIME-formatted file and submitting it to an SMTP pickup directory. When the email arrives in my inbox it has lost the opening double-quote of any double-quote terms. e.g.
<html lang="eng">
becomes
<html lang=ng">
I have checked the file before it is submitted to SMTP (PowerMTA) and it does contain all the correct double-quotes etc.
What's happening here, and how do I code around it? My end-users will be using this solution to create HTML-based outbound email, so it needs to cope with any HTML content.