Recently a client running zc v1.51 having problems with contact us email form not receiving to admin email address.
Testing showed the email was in the email archive in zen database.

Only column layout grid was installed and some CSS changes were made to the template.

Order emails would send without problems, contact us would not.

Upgraded to zc v1.54 tested as a stock install - same problem
Import and upgrade database from zc v1.51 - no errors - email problem remained

Again order emails would send just fine even the direct email from admin->tools->send email would send properly but the contact us form was not working.

Solution:
Log into cPanel, MX Entry, select your domain, choose Remote Mail Exchanger and it was instantly fixed - contact us form works order emails work.

Please note that this may not be related to your site or your host or your version of cPanel, but it was the only way to fix this problem with my client.