Why Cant I Get Emails From Hotmail On Redbrick

Why Can't I Get Emails From Hotmail On Redbrick

Originally it was thought that Hotmail had been added to a RBL that DCU's Computer Services Department was using.

... After further investigation it appears that it is an issue with Redbrick using different MX hosts for IPv4 and IPv6 email traffic:

• redbrick.dcu.ie. 86400 IN MX 80 scan1.dcu.ie.
• redbrick.dcu.ie. 86400 IN MX 80 scan2.dcu.ie.
• redbrick.dcu.ie. 86400 IN MX 60 mailhost.ipv6.redbrick.dcu.ie.
• redbrick.dcu.ie. 86400 IN MX 70 mailhost2.ipv6.redbrick.dcu.ie.

rfc 974 states:

"If the list of MX RRs is not empty, the mailer should try to deliver the message to the MXs in order (lowest preference value tried first). The mailer is required to attempt delivery to the lowest valued MX. Implementors are encouraged to write mailers so that they try the MXs in order until one of the MXs accepts the message, or all the MXs have been tried. A somewhat less demanding system, in which a fixed number of MXs is tried, is also reasonable. Note that multiple MXs may have the same preference value. In this case, all MXs at with a given value must be tried before any of a higher value are tried. In addition, in the special case in which there are several MXs with the lowest preference value, all of them should be tried before a message is deemed undeliverable."

It looks like Hotmail are only trying a fixed number of MX records (either 1 or 2) and then giving up on delivery (the ipv6 hosts don't have IPv4 addresses and it looks like Hotmail doesn't use IPv6 yet). Since the two lowest preference servers are IPv6 only addresses delivery fails.

I (redgiant) have raised the issue with Hotmail support and the Hotmail product team (15 dec 2004). Hotmail never got back to me about this issue. I gave up chasing it... If you know someone on the Hotmail team - bug them about it. ;)