You may think this is boring, but it’s what works. Leave the sales talk and the promotion for when you call them back. Leaving a greeting is all well and good, but if it has no context you’re going to struggle to stop the person from giving up on you. Make sure people know that they’ve reached the right place. Hello, this is the office of X, the Y department. Please leave your name, reason for calling, and I’ll get back to you as soon as I can. By mentioning the specific department or office they’ve reached, you’re reminding them that they’ve reached the right place, and this is not some generic support department they’ve been redirected to. We talk to lots of different people every day. Make sure you remind people of who you are, and why you’re the best person to handle their call (and more importantly their valuable time). Hello, my name is X, the Senior Manager of Y, I’m sorry I’m unavailable right now, but if you leave your number I’ll return your call as soon as I can. Not only have you revealed who you are, but you’ve also given them the reassurance that their call is important to you. It leaves the right impression. The order of your words can seriously impact how your greeting is received. Research shows that we remember the first and last items on a list best, so the statements that matter most are those at the beginning and those at the end. Hello, you have reached X. I’m out of the office at the moment. Provide me with your contact details and I’ll get back to you as soon as I can. Do you see how important the order of the words is? The name comes first and the call to action is last. Most people will put all this important information in the middle of their greeting. It may not seem like a big difference, but it really matters. It can be tempting to try to fit as much information into a voicemail greeting as possible. Don’t do that. Sometimes less is more. Try to incorporate some strategic pauses into your greeting, so you can let everything sink in. Hello, this is X from Y. [Pause] I am not available to take your call right now. [Pause] If you are calling about Z, then please leave your name and number and I will get back to you as soon as you can.
YouMail is an excellent voicemail app. It provides a highly user-friendly visual voicemail service. You can get your voicemail to email or even text. It also lets you forward or reply to voicemail. Besides, YouMail works as a smart call manager that prevents robocalls, entertains missed callers and more.

You could add the words "After-Hours Service" or "After-Hours Line" after the company's name. That way there's no concern over whether it is indeed a number that reaches a real person who will return their call during non-business hours. It's a way to let them know they're on the right track. If that makes sense. :)
Although I’ve spent some time tinkering with and learning Python over the last few months, I don’t have much experience with building apps that call third-party APIs, such as those from Twilio. Luckily, Twilio offers several Quickstart examples for a number of programming languages. And one of those examples shows to how to create a Python app that accepts incoming calls, plays a voicemail greeting and records a caller message. This is the Quickstart code that I tweaked for our project.