Normally I'd avoid arguing with your Reindl as it simply clutters the list. However you made some invalid points that need to be corrected for those who may browse the archives in the future.
On 5/9/2013 7:26 AM, Reindl Harald wrote: > if you have a A-record for "example.com" and you incoming > mail-server is on this IP you do not need any MX record > and postfix will happily use the A-record to deliver mail When did you last come across a domain configured strictly for fallback to A? While RFC may require it, and some used it in the 70s and 80s, no receivers rely on fallback to A in 2013. Anyone versed sufficiently in SMTP to know of the existence of fallback to A isn't going to rely on it. They'll have proper MX records. > another story is if there is a MX-Record but the listed > hostname does not resolve and at least for me the intention > of "if the MX does not exist" is not clear enough if it means > > a) no MX record for the domain > b) a MX record with a non-resloving hostname > > reject b) would be fine Only if the response is 4xx. People fat finger records all the time. > reject a) would be stupid If generic and not selective then yes, but not because of fallback to A. The real problem here is legitimate send-only domains, such as some mailing lists, bulk mail campaigns, emergency alert and other notification systems, etc. -- Stan
