Can you provide url of your site?

Sure, its kikcommunity.com

Hello Micheal,

I visited your site and tried out the conatact page, Everything is working fine.

Michael we have just tested it and we received the e-mail. 

Please check whether your cron jobs are properly configured as well as SMTP

I am having the same problem. Everything worked fine before but now all of a sudden it has stopped working. My cron job is the same as its always been when it worked before. When testing I get an error (mail not delivered) from yahoo.

OK, I have figured out that user email addresses with yahoo won't get through, but I tested it with an email address from Mail.com and it gets through! So its it must be an issue with yahoo, so that makes me wonder how many messages have I not been getting with users that use yahoo for their email address?

Hart, I'm sorry but we just tested it with yahoo and everything works as it should be. 

Where do you get the error 'mail not delivered' ? 

The contact us form looks like it works it even gives a message at the end that says "Your message has been sent. Editor will reply shortly. Thank you." but I don't receive the message at the email address I provided when I set up the "Contact Us" form plugin.

I got that error at my yahoo account, it was in my inbox. I only got that message once out of many attempts at testing the "Contact Us" plugin. My cron job is the same as its always been and the only changes is the recent platform update to version 1.7.2.

Hart, send a message via contact us plugin

before that open your database in phpmyadmin

ow_base_mail table see if the mail goes away from that table. Seems like your cron is not working. 

You can also check ow_cron/cron_error_log file if there's one, probably something is there too.