SendGrid doesn't send email to YAHOO?

Just a note on this in case others are looking into this. If you have done everything you can to ensure deliverability (such as Sender Authentication), there is still a chance your emails can get blocked. SendGrid (like all email senders) use a Shared IP address to send emails, if this IP goes on a Blacklist somewhere, then certain email providers may block it.

I have this issue with certain email providers (Outlook especially) with a shared IP I am on through SendGrid. It is expensive to move to a dedicated IP address, but this can help avoid the problem.

Some more discussion on this: https://news.ycombinator.com/item?id=14202068