Did you know that VDX can send email messages to your users? You can have preformatted text sent automatically when a specific update occurs or have free text message notifcations based on something specific you want your users to know about their interlibrary loan item.
The VDX User Alert message options have been around for a few years, and while your location may have opted not to use them before, you may want to take another look. With the high volume of requests that you may be processing, these messages can be especially useful when automatically triggered in certain situations or manually triggered with an with an action update. There is a specific action which will just send a free text message to your user.
Please contact Nick Banitt if you would like to add to your portfolio of messages. Some configuration must be set up for a location to use this functionality. I am happy to share ideas about what other libraries are doing or to help you think through any workflow implications.