Does SMTP allow URL attachments (not links)

SMTP allows attachments with local image files (haven’t tried it but it’s documented).

IOS Notifications permits a URL as an attachment (again, haven’t tried, don’t have an iPhone), which appear to pull the image and include as an attachment.

I can’t find a syntax that works for that in SMTP (though there are a few hints in postings that it might).

Does it?

Or do you need to shell a wget (or something similar) and use a local path?