Is it considered haram or theft for a translator to send his CV to international companies whose addresses he obtained from his work email, given his low salary and the employer's mistreatment?

What the questioner did, spying on the company's email and misusing it, is forbidden and a betrayal of trust, due to Allah's saying: "And do not spy." He must repent to Allah. As for the low salary and poor treatment, they do not justify betrayal. He can search for another job after his contract ends or with the employer's consent, or work as a freelance translator outside official working hours. However, corresponding with companies or making agreements with them during working hours is forbidden because his benefits (time and effort during work) are owned by the company.