Islamically speaking, there are two certain restrictions from the Sunnah (both can be disputed) when it comes to men and women interaction, everything else is pure speculation and what could be bad for you (opinionated).
A person can not touch the skin of those who are not muharam to them
Being alone with that person - Not in public, chat rooms, etc..
The Prophet (saws) said, "Whenever a man is alone with a (non-mehram) woman, the Shaytaan makes a third." [Source: Al-Tirmidhi Hadith 3118, Narrated by Umar ibn al-Khattab]
This includes private chats, private email accounts, sitting alone in a room, etc.
Everything else is OK, like talking to a woman that is not a non muharram even if that isn't needed to (school work groups, friends, etc..). There is nothing wrong with mixes of the sexes in Islam (that is a culture forbiddance) as proved by the Sunnah of the prophet.