RSTでMXフォールバック(secondaryへの再送)しないMTA

WebShield (McAfee)
Fortigate (Fortinet)

RSTによるMXフォールバックを確認したMTA

sendmail 8.12.11/8.12.11/Submit
         8.12.10/8.12.10
         8.12.10/3.7W
         8.11.6p2+3.4W/8.11.3/smtpfeed 1.14
         8.9.3/3.7W-1.1.1.1.2.1
Postfix 1.1.3
Postfix 2.1.3
Exim 4.32 (megatron.ietf.org)
qmail-1.03  (但し、FINではfallbackせずprimaryに再送)
Gmail
Xserve/MantshX 2.0 (smtpout.mac.com)
Switch-3.1.4/Switch-3.1.0 
Melon SMTP Server 1.40.0.1
Radish 2.2.8
Radish 3.0.0.-b026

   When the lookup succeeds, the mapping can result in a list of
   alternative delivery addresses rather than a single address, because 
   of multiple MX records, multihoming, or both.  To provide reliable
   mail transmission, the SMTP client MUST be able to try (and retry)
   each of the relevant addresses in this list in order, until a
   delivery attempt succeeds.  However, there MAY also be a configurable
   limit on the number of alternate addresses that can be tried.  In any
   case, the SMTP client SHOULD try at least two addresses.