[tehwalrus]

No, no...

They do read all the letters (at least, the researcher does.) It is only the first signal.

A handwritten letter isn't in itself an indicator - someone may simply have not had much time - if the writing is difficult to read, or if it's several pages long, then we're into danger territory.

Generally the MPs first see their mail alongside their researchers' draft responses to them. They do need to know what they wrote back to everyone so that if they meet the constituent at a Surgery they will know what they're talking about.