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
• There was a temporary DNS issue with the receiving server. 

DonorView will automatically unsubscribe soft bounces if the message has not been successfully delivered after retrying for 48 hours.