"保持书信往来"译成英文怎样讲

communicate with
I communicate with him regularly by letter.
我经常与他通信。

如果是在回信，就是keep in touch!

如果不是，就写：Do write to me.

如果很正式，就写：Please keep contacting me by mail or Email.

这样翻：

keep in contact via mails

Keep in touch or keep in contact!

keep in touch with sb.