Письмо на другу желательно с переводом

Thanks (a lot) for your (last) letter.  

Your last letter was a real surprise.  

I was glad to get your letter.  

It was great to hear from you! / It was great to hear that… / I was happy to hear…  

Вы можете также извиниться за то, что не писали раньше:  

Sorry I haven’t written for so long but …/ Sorry I haven’t been in touch for so long.  

I'm sorry I haven't answered earlier but I was really busy with my school.  

и/или упомянуть какой-либо факт из полученного письма:  

I’m glad you passed your History test!  

Sounds like you had a great time in London!  

Great news about your…!