Just ask them to email you the article or find a working plugin.

Check this free one I found > WordPress › Guest Posts « WordPress Plugins

First you should ask yourself what you expect to gain from offering guest posts on your site. If you think it will bring you bucket loads of traffic then you can think again.

If you are going to do it then be VERY strict with your quality guidelines:

- don't accept articles that are not related to the topic of your blog
- don't link out to non-related sites even if the article is related
- make sure it is written in such a way as to actually engage your current audience
- make sure it is of a decent length (800+ words)
- make sure that authors have a Google+ profile and link this to their article

In all honesty though, you'd probably be better off writing content for your site yourself.

If you are offering guest post opportunities as a way to add more content to your site, this will just be a headache for you because you need to come up with guidelines to ensure the post submitted to you is not copied or spun content. This will take away your precious time, better create your own content because you have 100% control over quality.

If you are offering guest post opportunities for a cost, be careful because the latest google news is that sites offering guest posts can now be penalized.

Getting engaged with other bloggers within your niche and invite them to post in your blog. The easiest way to get engaged with them is by commenting in their blogs.

Make friends with other bloggers and email them directly for an opportunity to guest blog on your URL.

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By the way Matt Cutts just recently announced that guest posting might get you penalized...

You should check out Myblogguest and their wordpress plugin (free) for publishers that allows you to accept posts to your website.

If you wish to post to other sites you have to pay ($90 per month) for larger plan.

Bloggerlinkup is also a very good resource (sends out emails of people seeking and accepting guest posts)

What is your subject about? I would love to guest post with you. Just PM me so we can discuss this further.

If you want to get guest post, then be careful about the subjects, topic and post quality. Because low quality and irrelevant can penalize your website.