The mail from Lin you actually get by doing things with Alex, when she is having a bit of a crisis about all the blowjobs she's giving, if you direct her to Lin, you will get an update in mail form.
For Lina:
1 is sent automatically at the end of the run if you have Jenny Prey and 4 Love as well as Lina at 4 Nerve.
2 is asking her for a photo to masturbate too when getting photos for Haily.
5 you get by trading a photo with Lina during Haily's special photo trading. However depending on how much Sami likes you... you may get one of her instead.