When Twilio SendGrid receives your email request, we look at the domain used in the
From (sender) email address, and attempt to match it to the domain set in Link Branding for your account. For example, a sending email address of
firstname.lastname@example.org would match the Link Branding of
url1234.mysite.com because they share the domain of "mysite.com".
From (sender) email address domain does not have Link Branding set up, Twilio SendGrid instead uses the default Link Branding, which is
sendgrid.net. If you want emails to have a default Link Branding, you must flag one of your Link Brandings as Default.