Correct

来函

/ láihán /
Strokes

Definition

incoming letter/letter from afar/same as 来信

Example

As a Noun

incoming letter; letter received

1
Láihán
来函
jìng
敬悉
  
,
chí
迟复
wéi
qiàn
  

I'm honoured to have received your letter, and sorry for not having been able to reply earlier.

As a Verb

send a letter here

2
Qǐng
láihán
来函
gàozhī
告知
zhǔnquè
准确
日期
  

Please inform us of the exact/precise date by letter.

3
Duìfāng
对方
lián
lái
shǔ
hán
xúnwèn
询问
xiángqíng
详情
  

The other party kept writing to us to inquire the particulars.