Very personal. Used between lovers, family and close friends.

非常私人的，一般在爱人、家人或者给非常亲密的朋友写信的时候使用。

Very casual. Used between friends. Can be used between coworkers if you want to appear very casual, at the risk of sounding unprofessional.

一种较为随意的结尾，一般在与好友通信是使用。如果你希望看起来平和一点，也可以用于和同事的通信。不过这样的结束语不太正式，会显得不够专业。

Casual and used between friends.

适用于朋友之间通信。

'Thanks' is very casual and 'Thank You' is formal. Usually used in a business setting. 'Thank You' is a great way to end an email to a stranger, especially if you are making a request or asking a question.

Thanks偏随和，而 Thank You 比较正式，常用于商务场合。当你给陌生人写信，尤其是请求协助，提出要求或者询问事项时，用Thank You是收尾的好选择。

Casual or Business casual. A more personal, but still polite way to end the letter. You've probably met the recipient in real life.

日常交往或者商务场合都可以。 它算是一种比较私人的结束语，但同时也可以体现出你的礼貌。一般用于你之前见过面的对象。

Casual or Business casual. A polite way to end the letter. Can be used between friends or strangers.

日常交往或者商务场合都可以用，是一种礼貌的方式。对朋友和陌生人都可以用。

Casual, Business casual or Formal. The standard letter ending. 'Sincerely' is the most versatile ending because it can be used to end either casual or formal correspondence. If you're unsure about how to sign your letter, use 'Sincerely'.

日常交往、商务或更正式的信件。 是标准的信件结束用语。 "Sincerely" 是使用范围最广的一种结束语，无论日常和正式通信都可以使用。如果不确定怎么结尾署名，就用sincerely吧。

Business casual or formal. You would use this if the recipient is someone you haven't met in real life.

适用商务或更正式的信件。 如果你和收件人之前并不认识，或未在生活中打过交道，您可以用这两个词来结尾。

Formal. Used in business correspondence when the topic of the letter is serious. Sometimes used if there is a conflict between the sender and the recipient.

正式的结束用语。 当信件的内容是非常重要的时候或商务谈判时可以使用。当你和收件人之间有分歧或者冲突的时候，也可以使用。

Using an ending that is too casual for the situation may not always be inappropriate. Conversely, using a casual ending can show your self-confidence. But to do this requires you to gauge whether the recipient would like a more casual conversation.

在正式场合使用一个随和的结尾并不一定意味着什么不恰当的事情。有的时候，这样做可以显得你很自信，谈话很随和。不过在这样做之前，请一定要了解一下对方是否喜欢这样一种随和的方式。