Travelers that have obtained a Schengen visa in the past 59 months and have a valid United States residence status are eligible to mail-in their applications. This means you can ship your passport and get your visa back via post, and avoid the in-person interview. There is no need to inform the consulate ahead of mailing in your application. However, mail-in applications have 2 additional requirements:
The filled visa application has to be notarized by a notary public.
The application has to be shipped to the appropriate consulate along with a pre-fixed return label addressed to you.
Only certain Schengen countries allow you to mail-in. Currently, these include Germany and Switzerland.