We're seeing a few reports in Blogger Help Forum: Something Is Broken about problems with email, sent by Blogger, when the destination is a non GMail email system. Some email systems verify the sending email address, against IP address. With these systems, email which originates from a Blogger account that's based on a non GMail email address, and comes from a Blogger / Google IP address, is going to present a problem, to the account owners.
What Blogger won't tell you