I assume that you managed to run the SendGrid API through Node.js, since you tagged the question with an Express tag.
I'm currently trying to create a transactional email template using SendGrid, and I succeeded.
, .

. . .

.

html, . .

" ".

. . Node.js- .
mail.personalizations[0].addSubstitution(new helper.Substitution("your-subtitution-tag", "image-url"));
: https://github.com/sendgrid/sendgrid-nodejs , .

- . . , !