How big are your invoices? I generate PDFs both from code and HTML, and in general even the largest ones aren't above 500kb. Usually around 100-250 pages.
The invoice includes scanned bills of lading we get mailed in from our drivers. An invoice size can range from around 2.5mb to 12mb+. An we usually try to batch multiple invoice per email for their convenience. Things like 9 pin printer and colored copy paper bloat the sizes even with max size reduction enabled.
Makes sense. It would be cool if email providers could just convert an attachment into a link so it can still be sent over email for those large files.
Apple's mail program does this. If the receiver of the email is also using Apple mail, the link aspect is transparent. I've only had to use it a few times, but it was wonderfully helpful.