Things have become a little more tenuous in the email ecosystem of late. What was once a given, inbox placement is now hard fought.
Way back in the year 2000, blacklists had so many false positives, inadvertently (and sometimes intentionally (vertently?)) blocking email from legitimate senders that the notion of whitelisting sprang up with the creation of Habeas.com.
Office365/EOP IPv6 changes starting today
2 days ago