Creating a new email: HTML upload vs. send from ESP
We highly recommend sending in your email directly from your email service provider (ESP) to start an email in Litmus, as many times ESPs can change/alter your HTML template before your final send. Since Litmus does not alter your HTML code, you may see a difference between an HTML-uploaded copy versus what you see on your ESP’s sent copy. If you use the Update Proof & Previews tabs from Builder that is also not as accurate as sending the email directly from your ESP. We recommend that you make edits to your email where you build. If you build your emails in your ESP, it is best to make all edits there and send the new version of the email into Litmus using your unique Litmus test address.
If you send in your email directly from your ESP, you will see exactly what your subscribers see when they receive your campaign. You can easily send in an email test to Litmus from your ESP by using Litmus’ email addresses in the test/preview email send before sending your campaign to your subscribers.
Sending from your ESP is also best when using our Spam Testing tools, as this will provide the most accurate reputation scoring for your email. When you send from your ESP vs upload your HTML you'll also automatically get 7 essential spam checks in Checklist. This will help you make sure your authentication records are set up properly, including DMARC, DKIM, and more, in addition to making sure you're not on any blocklists. You can find these results in the "Spam Testing" section at the end of your Checklist. Read more about starting a spam test using ESP connection in this article.