Even if you do everything right, sometimes an email will not go through to its intended recipient. This is called a “soft bounce.” In many cases, the email client (e.g., Gmail, AOL, Yahoo, etc.) will try to redeliver the message several times over a period of hours or days and will only consider it undeliverable after the retry process times out. The reasons for a soft bounce include: The mailbox is full or has recently received an unusually high volume of email, the message sent is too large and has exceeded the limits of the receiving server, or there was a temporary DNS issue with the receiving server. AssociationSphere will automatically unsubscribe soft bounces if the message has not been successfully delivered after retrying for 48 hours.