MIME has been an IETF standard *since the 90’s* ; and still it’s astonishing how many mail clients simply do not support (or correctly support) the standards.

When Apple first released OS X, the built in mail client quite rigorously supported the IETF MIME standards, which, among other things, support multiple interleaved attachments and multiple attachments with the same name, but different types.  I could send an email that had multiple attachments: text—picture—more text—picture—styled text—picture—text-word doc-text and it would be correctly displayed on the recipient’s system in that order; if their mail client supported  the relevant standards.

LOTS of mail clients did not (and still don’t) support this, so when people sent , for example Word docs, which on the Mac at the time consisted of a file with a data fork and a resource fork (which in itself was a violation of Apple’s guidelines….data files were not supposed to contain resource forks!) both with the mywordfile.doc name, lost of mail clients choked because they were not coded to accept an email with two attachments of the same name.

Apple ended up having to add an option to the program to ‘send Windows-friendly attachments’ to enable this to work, even though their implementation of the IETF standard was actually the correct, by-the-book one.  

(and the less said about MS’s ham-handed attempt to make everyone use their client by inventing a totally non-standard "rich text” format the infamous ‘tnef’ file,  the better)

To this day it’s present in the 'Edit-> Attachments’ menu, but is grayed out and selected if you’re connected to an Exchange server. If, however you’re connected to a different email service it can be unchecked, which may be what happened here. The attachments are just .png files. (actually, Mac screenshots to judge by the file names )

Today’s history lecture brought to you by the words ‘No’ as in ‘No attachments on the list’ and the word ‘Link’ as in 'links always work' :-)