What is the Shariah ruling on my current job, which requires me to communicate with a foreign man via phone and internet for work matters, and is this job considered wrong or sinful?

It is permissible for a woman to work and produce, provided she adheres to Islamic regulations and etiquette. Islamic law does not prevent her from acquiring beneficial knowledge or engaging in lawful work that does not contradict her nature, though her remaining in her home is preferable if she does not need to work, or if society does not need her work. Your described work via email is permissible as long as it does not require going out, traveling, mixing with non-mahram men, or being in seclusion with them. If your fiancé stipulates that you quit your job and you agree, he has the right to prevent you after the marriage contract. If you stipulate that you continue working and he agrees, he does not have the right to prevent you as long as the work is lawful, for "Muslims are bound by their stipulations."