Yesterday, I updated my device to OS 4.5.0.174, wiped it and didn't use a backup, just set up it all from scratch. Now, everything seems to work smoothly. I can send and receive e-mails normally and I love my berry again.
Thank you VERY much for you time and your help.
Glad to hear you got it all sorted out @ngel, though it's a shame we cant identify the root cause. Clearly something on the device was the issue though.