I want to attach multiple PDFs to an e-mail, list them as both file attachments and also link (<a href="cid:referenceToAttachment">Open PDF</a>) to them within the text/html body.
Unfortunately, I can't seem to get both to work in Thunderbird (version 68):
If the attachments are part of a multipart/related boundary along with the html-body, the files are no longer shown as attachments at the bottom of the mail, but the cid-links within the html work.
If they do not share the boundary and are part of multipart/mixed, the cid-links no longer work, but the files are shown as attachments.
Content-Disposition of either inline or attachment doesn't seem to make a difference for Thunderbird.
I also checked this extension, but unfortunately it breaks the cid-links once I force showing the attachments
For other programs I checked, attachments always show up as attachments for either multipart/* type and the cid-links are either always broken (e.g. roundcube, k9-mail, ms outlook web) or just work (e.g. gmail, ms outlook).
Attaching everything twice, once within multipart/related, once in multipart/mixed would cause duplicate content for basically every other mail client.
How can I get this to work in Thunderbird?
P.S. I generate the e-mail using PHP symfony swift mailer (within Typo3)
