Is it safe to control a solid state relay from the MCU output?
Like you said, the relays need maximum 0.5 mA to operate. A microcontroller can typically supply 20 mA. What AKR failed to mention (and it's a reason why it shouldn't be the accepted anser!) is that you need to place a series resistor. At 3.3 V supply a 430 ohm resistor gives you 5 mA, which is safe for the microcontroller, and makes sure the relay triggers under all circumstances. For a 5 V microcontroller you need a 820 ohm resistor.