发出 + 信函
信函 (xìnhán) means "letter" or "correspondence," and is a formal term for written communication, especially in official or legal contexts. It is more formal than 信 alone. For example, 发出信函 means "to send out a letter."
公司今天收到了一封法院的信函。
Gōngsī jīntiān shōudào le yì fēng fǎyuàn de xìnhán.
The company received a letter from the court today.
请用正式的信函格式来写这封信。
Qǐng yòng zhèngshì de xìnhán géshì lái xiě zhè fēng xìn.
Please use a formal letter format to write this letter.
他负责处理所有来往的商务信函。
Tā fùzé chǔlǐ suǒyǒu láiwǎng de shāngwù xìnhán.
He is responsible for handling all incoming and outgoing business correspondence.