One more thing - whether it's ok to write "Dear [first name]" depends on the context of the letter, which you are not explaining.

If it is a business contact, not a customer and you've spoken with them before, then it's definitely ok to use the first name, and you can use "Hi [name]" or "Hello [name]" as a greeting instead. If so, you end with "Regards" or "Best regards" or similar. This is normal for business emails. If it is a friend or relative, or dating situation - likewise.

It's really only if it's a customer, or you never met the person before that it would be more appropriate to write "Dear Ms". For example you found out that you have a long lost relative in an English speaking country, or somebody wrote to you enquiring about professional services and you wanted to respond. Also in a an educational situation where this person was a lecturer, or some kind of expert that you are seeking advice from. Americans are the most relaxed about this, I think. Unlike some Southern Europeans, people will not be angry or mortally offended about titles as long as the tone of the letter is generally polite.

The bank, estate agents, the water company, solicitors, gas supplier the local council, state authorities etc are the ones who tend to use titles.

I look forward to learning all this in Russian! Not sure if anyone remembers my travel blog from Russian speaking countries where I got too informal, too fast with several people because I mistakenly thought it was ok.... Embarassing!! BLUSH!!!

"Dear Mr" type letters sometimes also end with "Faithfully" / Yours faithfully.
It sounds a bit stiffer to me though. Something a solicitor would write.