relay or programmatically through an API. • email address confirmations • password resets • purchase receipts • "thank you for [some action]" • monthly invoices
(Summly by Yahoo), features, products (Tumblr by Yahoo), talents, user base (Whatsapp by Facebook), brand name or trademark (Adidas by Rebook), Intelectual property (Motorola by Google) and similar reasons. Sometimes companies just decide to shut the product down.
your own custom domain instead of SendGrid's default settings. This will mask the header information of your emails with your data and will improve email deliverability.