It's not that strange. It's a relatively common issue. Depends on your WordPress hosting.
Though the plugin successfully sends millions of emails every day, there are a host of issues that can delay or stop emails on both the sending and receiving ends of a typical email. It depends entirely on your local configuration.
You will need to investigate this issue for your particular local configuration.
See Contact Form 7 Email Issues
Also current version of CF7 is 3.4.2. so you are well out of date.