As the other answers already suggest, the Pi is pretty much capable to serve these needs. It also also likely to survive its time (see also [here](https://raspberrypi.stackexchange.com/questions/325/is-the-raspberry-pi-suitable-for-running-continuously-24-7)). To add to the list of references: I have a remote data logging running 24/7 for almost two years now on a type B. The system's current uptime is 183 days, which is not even the Pi's fault.

However if you setup a mail server you might want to consider to not keep your mailbox solely on the SD-card but implement a backup scheme to regularly mirror it to another storage device. Rumor has it that power brown-outs may ruin SD cards on the Pi. 

Same goes for the chatlogs if you have an inclination to hold on to these.