Is it permissible to address the interviewer informally during communication?

Using 'you' (ты) during communication depends on the context, corporate culture, and personal preferences of the interlocutors. In a professional environment, especially in the early stages of acquaintance or formal meetings, it is customary to use 'you' (вы) to show respect and maintain business etiquette.

If a more informal atmosphere is established within the company or team, and the interlocutor suggests switching to 'you' (ты), then it is permissible. It is important to pay attention to the reaction and comfort of the interlocutor to avoid creating tension.

Overall, it is better to start with 'you' (вы) and switch to 'you' (ты) only after mutual agreement.