Hi, I've done GPIO programming for an OLinuxino board, very similar to RPi, and have extensive experience with Linux, embedded systems, and network protocols. Probably the easiest and most flexible way to do what you want is with some Python scripting, although I could also build a C++ app.
Using a cloud service has advantages for flexibility, but certainly it would be easy enough for the RPi to send email directly. I'm assuming you don't need to use the RS232 interface on your pressure sensors for this phase of the project.
So my bid is to provide a Python app to periodically monitor 4 pressure switches connected to GPIO pins, and send an email if any indicate overpressure (or on any change of states?, perhaps with a limit on the number of emails per hour. Input values can be written to a local CSV file with timestamps, which you can retrieve for graphing.
I will provide clean, efficient, well-commented code, and instructions on setup, configuration, and usage.
Thanks for considering my bid.