Being brutally honest ... I have never used the DM (Direct Message) feature on Twitter
and I never read DMs from other Twitter members. The reason is because right from my first day on Twitter, members began spamming me through the DMs, and periodic spot checks have proven that it has not changed in the years that I've been on Twitter.
DMs should be for private conversations that are REAL, not promotional messages. I experience this on other Social sites as well and usually ignore and delete the messages without responding.