HELLP PLEASE...another girl?

my bf broke up with me a month ago and i moved on and got a new bf and he started talking to this girl and i dumped the new bf bec i still liked the other one and weve been talkin and he says hes completly over that girl and they dont talk but i checked his v mail the other day and there is stuff from her like from 4 days ago i asked him and he saays their old should i believe him or not?