I've seen issues with specific email programs distorting the images - which had to do with settings on the email program on scaling images. Have you tried sending the email to different programs to compare? Like Outlook vs Gmail?
I haven't tried another email program. Did it display better when you used another program? I'm tied to gmail, since our whole organization uses it, so I'll have to figure out a solution on there.
The cases I've seen were it being distorted in gmail - but working in Outlook or Office 365. Once we'd figured out it was a gmail setting and it worked in Outlook the case closed out - I'm not sure what setting it would have been in gmail. I'm finding a bunch of Gmail support threads saying people are seeing distorted images in their email - but sadly none of them have a resolution listed.
We had the same issue and had to resort to saving it as a PDF and emailing it out manually :/