How to set up CORS policy for fonts?

In order to display custom fonts right in the email, the browser must receive font files with correct HTTP headers. If the server does not set required headers, some browsers can report errors in console or completely fail to display fonts.

To solve this issue your system administrator should apply the right CORS header for fonts on the server where they are placed.

Probably, your server is already configured, and you don't need to change anything. If not, you need to care about:

Correct mime-type headers
CORS headers — only if you serve fonts files & html pages from different domains
For IE, check that your http headers for the font files do not have no-store or no-cache.

Apache

To set right mime-types for font files, add these lines to config:

AddType font/ttf                         ttf 
AddType font/otf                         otf 
AddType font/woff                        woff 
AddType font/woff2                       woff2 
AddType application/vnd.ms-fontobject    eot

If you can't edit config, create .htaccess file in the folder with your project and add lines there.

For CORS headers add:

<FilesMatch 
    ".(eot|ttf|otf|woff|woff2)"> Header set Access-Control-Allow-Origin "*" </FilesMatch>

Nginx

By default, Nginx has no default mime types for fonts and wrong mime type for .eot files. Go to the folder with configs and find where mime types are defined. Usually, that's in the mime.types file.

Search .eot and string with it.
Add strings below.

font/ttf ttf; font/otf otf; font/woff woff; font/woff2 woff2; application/vnd.ms-fontobject eot;

For CORS headers, add something like this to your host config

location ~* \.(eot|otf|ttf|woff|woff2)$ { add_header Access-Control-Allow-Origin *; }