Use the following procedure to enable read receipts for all messages that an email account sends in Roundcube.
Do not rely on Read Receipts to verify if a message was read or not. It is possible to receive a Read Receipt for a message that was not read and, more commonly, it is possible to not receive a Read Receipt for a message that was read. It is also worth mentioning that Google specifically advises not to rely on Read Receipts to verify if a message was read. Please see the link to their documentation below for details.
In order to receive a Read Receipt back from the recipient, they must voluntarily enable the feature, and in some cases click a confirmation before the Read Receipt is sent back to you. If the recipient does not want to send the Read Receipt back, or if they don't know how to you will not receive the Read Receipt.
One specific example is the fact that the free version of Gmail does not support Read Receipts at all. It is only supported for the paid version of Google Mail and it must be specifically turned on in order to work. Please review their documentation here:
1. Login to Webmail
2. Click on the Roundcube Logo to login to Roundcube
3. Click on the Settings button in the left sidebar
4. Click on "Composing Messages"
5. Toggle "Always request a return receipt" to the on position
6. Click the blue save button