lammert - 2:45 pm on May 3, 2010 (gmt 0)
Mail servers will first query the DNS server for MX records. Only if no MX records are found, they will fall back to A records. [tools.ietf.org...] section 5.1.
A records for SMTP servers are deprecated anyway and are only still supported for compatibility with older setups.
catching email typos, ahum...