I have never experience using Arduino but I am thinking of using it for my project.
This project incorporates 5 proximity sensors and each sensor is assigned to a person i.e. Sensor 1 - person A, sensor 2 - person B, sensor 3 - person C and so on. When sensor is activated, email should be sent to the respective person. At one time, there could be 2 sensors activated and hence, email should be sent to 2 person.
I know that Arduino Mega2560 + wifi shield can be used to send email. But I don't know whether the above operation is feasible.
I'm by no means an expert, but I've been toying with a project that has enough similarities to share.
I have arduinos with sensors that update a web database via an HTML GET request. The server, after entering the sensor readings into the database, will email me to let me know it's working. The email portion is written in PHP on the server. If you have access to a web server with PHP, your project is very doable.
I could have had it email me directly, rather than going through the PHP on a web server, but I feared that I may put one at someone's house that has Sendmail/SMTP blocked by their ISP. Going through the web server gets around this potential issue.
Given that you can send an email to one person, you can send email to multiple people.
The only issues I can see are how you would specify the people to receive emails. If it's acceptable to hard-code the addresses in your sketch then that's easy enough, but if there's a hidden requirement to make this configurable then that would require a more complicated solution. But the email part is certainly possible, and of course there are lots of ways to make it configurable.
In my sketch, email recipients are coded in the PHP on the server, and it can go to as many recipients as you like. You can code it however you want, sending it to specific recipients based on whatever criteria you want. In my sketch, multiple Arduinos update to the same server, and each send a unique device ID. I could easily set the recipient according to what device ID sends the update.