I am developing an application in a developer organization which sends emails via POST requests using an external API.
Back in February or so I was able to send Salesforce Documents as attachments in my requests which would arrive at a recipient's inbox as an attachment which was expected. Now however, when I send a Document as an attachment in my requests, the Document/attachment doesn't reach the recipient's inbox, even though in Debug logs it shows all of the necessary content.
I checked the Base64 conversion string and it does convert back into a pdf with the expected content. Another thing that seems odd is the message size itself reflects the size of the attached Document upon arrival even though the attachment is not present. I am at a loss at this point as to what has happened and was wondering if anything has been changed to Developer Organizations that limit this type of functionality or if something else could be wrong. To update my Email Deliverability settings are as follows: