by letter

I could get no information from him by letter, either.

I mean it could have happened by letter or meeting.

The message might come by letter, as the first one had.

He asked me to live with him, and I agreed to by letter.

The members knew each other, but most communication took place by letter.

She became closer to her own mother by letter over the decades.

He didn't want us to hear the news by gossip or letter.

In the case of agents this should be by letter.

We have already made a request to that effect by letter to the President.

She died, killed simultaneously by letters from both the past and the future.