Earlier quoted context omitted.
I emphasise, do not rant - my partner worked in an MPs office answering the mail, you don't want to fall into that category, which is still read and responded to, but which is almost never actioned/considered seriously/even read (by the MP themselves) in any way. bad signs - all caps, more than a page long, written on a typewriter, hand written in illegible writing, etc.
Wait, why is "written on a typewriter" a bad sign? There seems nothing particularly suspicious about handwriting either, though as a practical matter, legibility might be a problem...
I once wrote to David Milliband (when he was foreign secretary) on the urging of Amnesty International about the upcoming international vote on the banning of cluster bombs.
I wrote it on a 1920s typewriter, sealed it with wax etc, as befitting a letter to one of the holders of the four highest offices, and never got a reply (although they did succeed in banning the use of cluster munitions - good!)
Later, when my partner was working for an MP, I mentioned the letter to her - and she laughed at me and said it would have been "one of those letters," because of the presentation - and that that's why I wouldn't have got a reply etc. ( I also made the mistake of writing directly to Milliband himself, and not to my MP asking him to pass it on, which is another reason I may not have got a reply.)
I fear this story makes me out to be all three of hipster, lefty and (worst of all) impressed-by-authority, so I predict all the downvotes in this forum, but it explains my earlier comment, so it's probably worth it for completeness.