To optimize performance, Spark Post sometimes may reduce the quality of the uploaded images.
In the past, when exporting for Adobe Illustrator, we have seen that exporting at a larger size and choosing "Type Optimized" as an anti-aliasing option has improved image quality.
The Post team is aware that Posts downloaded using Microsoft Edge and Internet Explorer 11 are blurrier than expected. We hope to resolve this soon.
For the time-being, you should see improved image quality if you download your Posts using Google Chrome, Mozilla Firefox, or Apple Safari.