When someone sends email message to both me and husband, the message goes to his mailbox and not mine My husband and I share one log-in account, with our own Mac pop mail account. When someone sends an email to both our email addresses, it goes to his mailbox, but not mine, even though my address is also in the "To" space.
When using POP usually the client deletes the email on the server after retrieving it. So the first client (yours or your husband's) will fetch it and delete it from the remote inbox.

You can tell the email client to keep the message in the inbox (Using a POP account with more than one device):


In Mail select Mail > Preferences.
Click the Accounts tab.
Select the account for which you wish to change the settings.
Click the Advanced tab.
Select the "Remove copy from server after retrieving a message" option.
Select a time frame from the pop-up menu.