Overnight in the US, the AOL Mail and Yahoo Customer Care teams both tweeted updates indicating services may be down.
No details on scope or ETA were provided, and in my own testing I was able to access my own AOL and Yahoo addresses. Both brands have indicated engineers are working on the issues and they will provide regular updates.
UPDATED 1pm EDT: around 10AM EDT the @AOLMail Twitter account indicated the issue was mostly resolved. My own Yahoo/AOL queues started to clear out around noon EDT, and unofficial word is that the issue is considered to be resolved at this point.