I had this situation where emails were not received anymore after I installed the CloudFlare plugin for WordPress. I installed CloudFlare so that the content of my blog would be cached “locally” for most visitors, as my blog is hosted in The Netherlands. After installing CloudFlare I started having issues with receiving emails. It took me a few days before I realized I had issues, as I barely check my Yellow-Bricks.com email account. After some troubleshooting I noticed it was only incoming emails that did no longer work. I checked the cloudflare settings, and I had already disable the proxying of the “mail” and “webmail” records, but still it didn’t work. Then I noticed an MX record entry that pointed to “mx20.spamshield.eu”.
I removed “mx20.spamshield.eu” and replaced it with the address of my mail server… And also removed the second entry for the MX record. After doing that emails started coming in again.