Earlier, the ClarkesWorld account posted a somewhat controversial tweet. Not controversial in the sense we’ve come to use so often, where it’s offensive or something, but involved actual controversy:
Just had to reject a story we wanted to publish because it had been self-published and distributed to 50 people. #dontletthishappentoyou
— clarkesworld (@clarkesworld) December 26, 2013
To be honest, this surprised me. Not that they had to reject a story on these ground, but because of people’s reaction to it. For one thing, published is published. I sold a story a while ago to a small SciFi group in Seattle for their newsletter.
That’s still published.
Or when I started this whole thing, I had a blog where I posted drafts of 3024AD stories.
Yup, also published.
Because what Clarkesworld and most others are paying for is first rights. They- and, more to the point, their customers- are paying for a story that no one else has read anywhere else, no matter how large or small that number is.
But, you may say, some places do it (or, don’t consider self-publishing to be published, or what have you). And that’s as it may be, though less common. Some places do buy reprints- in fact, there is a decent market for them. However, (and this follows the theme of this post) read your original publication rights- you have likely sold them for a period of time, be it six months or a year. So by selling the reprint rights, you may be violating those.
#dontletthishappentoyou
With rare exception (at least, rare exception among credible publications), there is a pretty simple way to tell: Read the submissions page. It’s all right there. In fact, it’s the fifth point on Clarkesworld’s guidelines:
Rights: We claim first world electronic rights (text and audio), first print rights (author must be willing to sign 100+ chapbooks), and non-exclusive anthology rights for Realms, the yearly Clarkesworld anthology.
We purchase First Serial rights and electronic rights. 120 days after publication, most rights revert to the author, but we retain the right to continue selling back issues of the magazine, the right to archive your story, and non-exclusive anthology rights.
deanfortythree 
Honestly, this is all news to me. I hadn’t thought of first whatever rights, etc. I don’t submit much, granted.
#thisiswhyIwillforeverbeabeginner
We all have a lot to learn! And I think most people don’t, and, honestly, this is probably a post that didn’t need to be written ten years ago. The landscape has changed so much that it doesn’t matter if you’re just beginning or have been around for years. The validity of self-publishing and the reach of digital distribution have altered the dynamic so much that these things have to be considered differently than before.