attach images to email

Set SMTP_EMBED_IMAGES option to false if you don't want to attach images
to the mail.

NOTE: If you have customized the template files `email_header.hbs` and
`email_footer.hbs` you can replace `{url}/vw_static/` to `{img_url}`
to support both URL schemes

.env.template

@@ -367,6 +367,9 @@
 ## but might need to be changed in case it trips some anti-spam filters
 # HELO_NAME=
 
+## Embed images as email attachments
+# SMTP_EMBED_IMAGES=false
+
 ## SMTP debugging
 ## When set to true this will output very detailed SMTP messages.
 ## WARNING: This could contain sensitive information like passwords and usernames! Only enable this during troubleshooting!