The reason for the bounce will be found at the very bottom of the notification. There will be a message from the recipient’s mail server that contains an error code, and a brief description that may or may not be helpful.
The most common reason for a bounce is the email address does not exist. This is normally due to a typo in the email address. These will say something like “501: bad email address”, or “501 5.1.3 Invalid address” or “515 destination mailbox address invalid”.
The second most common reason is that the message was flagged as spam. Every mail provider’s spam filter works a bit differently, and what gets flagged by one, might not be flagged by another, but there are a few things that can help you avoid getting flagged:
- Ensure you do not have any incorrect email addresses (the more bounces you get, the more likely you’ll be flagged as spam)
- Make sure the content is relevant, and the attachments are not too large or too many.
- Have your volunteers add your email address to their contact list.
- If a message does end up in a volunteer’s junk/spam box, ask them to mark it as not junk/spam in their email program. (This will help teach their mail providers algorithm to not consider your messages spam).
These bounce messages will typically have an error code of 541, but not always, and it will say something like “The recipient address rejected your message”.
Sometimes a mail server will silently reject a message as spam. This means a message might not end up in a recipient’s inbox, and you might not get a bounce notification. This is most common in corporate or government networks. Unfortunately, in this case, there is very little that we can do, the recipient can attempt to talk to their mail provider to ensure your messages come through, but as an external provider we are unable to control this situation at all.
This Wikipedia article goes into detail on what the various codes mean. https://en.wikipedia.org/wiki/List_of_SMTP_server_return_codes