Twilio SendGrid tracks email opens by inserting a small, transparent, one-pixel image at the bottom of all messages. When the client application loads images, it pulls the image data from Twilio SendGrid servers, and registers an Open event.
Untracked email opens
Not all email clients load images by default. There may be many occasions where recipients will have received a message, opened it, and even clicked on a link, and it will never be counted as opened. The following common email clients are known to automatically block images from loading by default:
- Apple Mail
- Google Gmail
- Microsoft Outlook
- Mozilla Thunderbird