wcSMTP and "no MX" error

Here is how a SMTP sender works:

Given the E-mail address X@Y where X is the user id and the Y is the domain:

Issue a DNS query to return all the MX records for the domain Y.
The MX record is the post office IP address for the domain. A domain can have more than one MX record. For example, the MX record for santronics.com is mail.winserver.com
If no MX record is found, the RFC recommendation says to try "atleast once" and then bounce the message if not successful.
See the note below for wcSMTP implementation of this rule.
For each MX record found, try to connect to send the message.
If the first one fails, try the next one, etc. This process continues until it succeeds or the number of "attempts" as defined in SMTP setup is reached. When the attempts is reached, the message is bounced.

Note:

RFC recommendation on how to handle an E-mail domain address that does not have an MX record is to "try atleast once" using the domain address to remote SMTP server. If it fails, then bounce it.

Now as far as Wildcat is concern, when we enforced this recommendation we found it was problematic for many of our sysops because for one reason or another, the problem was more about DNS setup. The DNS MX lookup was not reliable and/or the DNS server might be down.

This RFC recommendation was programmed into wcSMTP in earlier versions. However, Santronics relaxed the logic in subsequent updates (AUP 447.5) due to customers who have domain names with temporary down times. So wcSMTP was relaxed to follow the normal mail retry options defined in wcConfig SMTP setup which by default is 72 attempts (once per hour) before a bounce message is sent.

But some customers with more reliable 24x7 operations want a more immediate bounce response especially in situations where the E-mail address simply had a typo. As one Wildcat! administrator at a company said: "Our boss didn't want to wait 3 days to find out he had a typo!" So the following new (AUP 449.4) command line (and registry) options will enable or disable the RFC recommendation of "No MX, Try once" logic in wcSMTP:

/nomx-

No MX refound, follow the Retry limits (default)

/nomx+

No MX found, Try once

via the wcSMTP registry folder:

DWORD value "NoMxTryOnce" 1=Enables, default OFF