You can see email delivery issues on the Voters (or Officers) tabs of your poll. For example, in the following image, you can see there is an issue with the email to Albert because there is a red exclamation point icon beside his email address:
The red exclamation point indicates a problem.
The green checkmark tells you that BallotBox has not received any indication that there is an email delivery problem. (A green checkmark does not, unfortunately, mean the email was received. For example, if a spam blocker incorrectly marked BallotBox's email as spam, the spam blocker may not notify BallotBox that the email was not delivered.)
If you click on that red icon, you can see a detailed email delivery report, such as this one:
We recommend that Admins check their Voters tab for email delivery issues so they can decide how best to address them.
To do that, you can filter the Voter list on a number of bases.
These are the filters available by clicking the Email button on the Voters tab:
A "temporary" email problem may resolve itself, but it does mean the email message has not yet been received.
A "permanent" email problem will not resolve itself. Examples would include the email address having a typo in it, or the person leaving that organization and the email account being deactivated.
If you'd like to download an Excel file that lists those voters who have email problems, click the Email button at the top, and select With email problems, and then at the bottom of the window, select the Export Voters button.
You can then open that file in a spreadsheet application (such as Microsoft Excel), and see how best to get emails to those voters. Once you have corrected the email problems, you can import those voters with their revised email addresses so BallotBox can communicate with them.