Running my site against DNSreport.com results in the following complaint:
WARN: One or more of your mailservers does not accept mail in the domain
literal format (email@example.com). Mailservers are technically required
RFC1123 5.2.17 to accept mail to domain literals for any of its IP
addresses. Not accepting domain literals can make it more difficult to
test your mailserver, and can prevent you from receiving E-mail from
people reporting problems with your mailserver. However, it is unlikely
that any problems will occur if the domain literals are not accepted.