I have Verizon FIOS with a POP3 email account, which is configured on several PCs and my smartphone. Monday I contacted support by phone about lost incoming emails on all the systems. Four of them were emails that I bcc'ed to myself earlier that day and never received. There was also one that my sister-in-law sent the day before that was never received on any system. The support tech told me that sometimes Verizon decides to block some incoming emails for various reasons. The tech then told me how to "whitelist" the senders that were being blocked. I did whitelist the senders that I knew I has lost emails from. What I don't understand, is how I am supposed to know what important emails I didn't get? If Verizon is going to do this, they should email me a list of the senders they decided to block, so I can review the list and add important ones to my Verizon whitelist.
That said, evidently Verizon doesn't realize that their subscribers depend on email for important communication, and should act more responsibly. If their servers are too busy at a given time, they should queue the messages for future delivery. If messages are dropped because they suspect spam they should allow the subscriber to see what was blocked, and have a chance to retrieve the messages.