Keep it simple, concise and to the point. Callers won’t need your life story, and won’t want to wait around for a 2-minute greeting to end just so they can leave a message. Don’t hide the details, tell them where you will be, when you will be there, or when you won’t be there, and how to get in touch.
If your caller has left you a detailed message with their query, it enables you to get straight down to business when you reply.

1.) Siete connessi alla mailbox di John Doe. Attualmente il Signor Doe non è disponibile. Potete richiamare più tardi o lasciare un messaggio con il vostro nome e numero di telefono e il Signor Doe vi richiamerà al più presto possibile.
Users often don’t invest enough time into their messages, resulting in incomplete, unprofessional, or otherwise under-whelming greetings. Sure, crafting a greeting doesn’t sound all that complicated; however, there are a number of pitfalls users can fall into—i.e. informality, terseness, sincerity, lack of direction, and more. While none of these sound too catastrophic, they are often interrelated. As such, they tend to worsen any problem. For example, humor can cause informality, worsen ambiguity, and weaken sincerity. That being said, users should strive to avoid ALL these pitfalls.