Gmail for Business offers the option to verify whether an email has been read by the recipient. As a G Suite administrator, you can make this possible by enabling Email Read Receipts in the domain accounts. 

During configuration, you will see the following options:

• Do not allow read receipts to be sent: This option disables the use of read receipts within the domain.
• Allow email read receipts to be sent to all addresses in my organization as well as the following email addresses: This option will restrict read receipts to be used only internally with the addition of up to 100 external emails. Once enabled, you can write the external addresses allowed by separating them with a comma. There is also an option to manually confirm with the user when there is a read receipt or if they should be sent automatically.
• Allow email read receipts to be sent to any email address: This will enable read receipts for all internal and external email addresses, but will confirm with the user every time there is such request. These options are demonstrated in the following screenshot:

Now that your users can use email read receipts to confirm that someone read an important message it's time to learn how Mail Delegation can help users during their vacations.