RS232 ESD Protection

I do not think MSP430F5437 has any "RS232 lines". As a mater of fact, I am not aware of any MSP430 chips that has "RS232 lines". Which pin numbers on the MSP430F5437 are you talking about?

Sorry,

I meant UART communication (RX, TX in the MSP430F5437IPN it's pins 56, 57)

The UART lines have the same level of protection as other I/O lines of the chip. See the data-sheet. Unlike RS232, all the I/O lines are for inter-connection on the same board, or between close-by boards in the same enclosure. RS232 is for intra-connection between different enclosures and requires much better protections. The UART line do not have the level of protection as required by the RS232. Also, the voltage levels of the signals are different. A UART to RS232 level converter must be use. And the level converter will provide the extra protection required for RS232.

All MSP port pins have a clamp diode against VCC and VDD. It takes up to 2mA rated current. Independently of their use as GPIO or UART or whatever. I'm not 100% sure if this applies if the pin is used for analog usage and the digital logic is disabled, but maybe still.
VCC/VDD need to be able to swallow this current (which may still be a problem on low-power designs) or VCC might raise above the allowed limit.

These clamp diodes will not protect agains high transients, however (limited by the diodes response time, typical Schottky ones, I think)

If you're using real RS232 connections (that means V.24 +-3..12V voltage levels), then the level shifter (MAX232 or similar) should implement the ESD protection (there are many variants with different protection levels, usually labeled as 'E' type in the name postfix)

Thanks