email

Gmail

Gmail

Google's email client and the inbox most people mean

Gmail's search is still the reason to use it. Conversation threading, effectively unlimited retention on paid plans, and spam filtering that most self-hosted setups cannot match make it the default even for people uncomfortable with the arrangement.

SendGrid

SendGrid

Transactional and marketing email delivery

SendGrid handles the part of email nobody wants to own: reputation, authentication, bounce processing, and the endless negotiation with inbox providers about whether your mail is wanted.