Will emails be dropped if a single MX record is missing?

I'd like to setup email using Google Apps for your Domain but can only enter 5 of the 6 required MX records due to limitations with number of host records I can enter (I'm using Zerigo DNS to host my DNS records):

aspmx.l.google.com

alt1.aspmx.l.google.com

alt2.aspmx.l.google.com

aspmx2.googlemail.com

aspmx3.goog开发者_开发知识库lemail.com

aspmx4.googlemail.com

aspmx5.googlemail.com (this one is not included)

Will emails be dropped if that last MX record is missing? What are the implications of not including the last MX record?

No. When a mail is sent to your domain, the sending mailserver will use exactly one of the servers in the MX records. Any of the servers you name can accept an e-mail, there are just many of them to do load-balancing and fallback.