James E. Pratt wrote: > > Bob Proulx wrote: > > >What would have been the downside of *not* having a backup MX? The > > > > Loss of mail. > > No. "Possible mail loss" is really the correct term. Just because I have > no backup MX, it does not mean I will lose mail.... (Mail loss can, and > usually is caused by many more issues than just no backup/secondary MX).
Loss of mail cannot result solely from a primary MX being offline. If you believe that it can then let me ask a related but different question. Does your mail server ever return a 4xx code such as: - out of disk space / insufficient system storage - dns temporarily unavailable / domain service not available - service not available - mailbox not available - user quota exceeded - too many simultaneous connections - other If the mta does ever return such a code then (for the sake of argument) the same potential for mail loss exists. If you believe that this causes loss then you would want to ensure that none of these conditions can ever happen. Of course this is impossible due to practical limits. Fortunately for us mail transfer was designed to be robust in the presence of these problems. When a mail transfer agent receives a 400 level response it knows the action was not taken and the condition is temporary in nature. The mta retry interval should be at least 30 minutes. The mta should give up retrying after at least 4-5 days. Bob
