Some Comcast emails suddenly being blocked

Hello @MaryJoC83 ,

Based on similar issues I've seen in the past, this could be one of two things. 

During holiday and US election seasons, many email programs and IPs will begin throttling email deliveries due to the high volume. This can, depending on the receiving IP, result in bounces like Undeliverable, Blocked, or Other. Since it's so sudden for you, this is the most likely situation. However if the blocked bounces continue to occur with each sendout, then the more likely issue may be the one described below.

While we haven't gotten a particular announcement like we did with the upcoming Gmail and Yahoo changes, another possibility is that changes to Comcast's anti-spam algorithms may be resulting in increased filtering / bouncing. If your from address has a unique domain (rather than a free one like Gmail, Yahoo, iCloud, etc.), then its delivery may be impacted if you haven't set your Constant Contact account up for self-authentication. With all the delivery gatekeeping and anti-spam/malware safeguards in place nowadays and going forward, it's necessary for businesses using an ESP to have this in place. 

If you'd like specialized insight regarding your account's delivery settings and these particular contacts, I'd recommend speaking with our Delivery team.