A handwritten address carries a kind of attention a saved contact does not require.

Effort is a message in itself. Writing out an address means holding somebody in mind for a full minute, getting the details right, and accepting that it cannot be undone with a backspace, none of which is required when a name is simply selected from a list. The content may be identical; the attention is not, and attention is what the receiver is reading.

Send one thing by post this month to somebody who would not expect it. The words matter less than you think. The fact that you sat down and did it is most of what will be received.