Do students of English and people using English at work, especially those who write business letters and emails, follow the existing rules for writing business correspondence? It has been written a lot about the level of formality typical for particular letters, its social function and aim, and the use of stylistically relevant features. But as the pace of our lives is becoming faster and faster these rules are less and less obeyed and considered important. The work tries to uncover whether the level of formality and familiarity has the influence on people involved in writing business letters and what their opinion about its use is, what impact and impression they get when leading business correspondence on different formality levels, and what kind of relationships it signals. Everyone who is not lax about their writing and does not want to follow the mainstream of simplified use, or just does not know how to improve their correspondence skills may find this thesis as a helpful and practical guide. The study is supported with research, all the findings are clearly demonstrated by bar and pie charts and a number of line graphs.