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Re: SRV records

2005-12-08 19:23:48

On Dec 8, 2005, at 5:22 PM, Markus Stumpf wrote:

is anybody aware of MTA software that uses SRV records for mail routing
(in addition(?) to MX records)?

I don't know about the status of 2821bis - should they be mentioned?

Perhaps in respect to HELO/EHLO verification. : )

Should there be a precedence of SRV records over MX records? Should
MX records become obsolete?

While SRV records allow greater control over issues related to load balancing, SRV has a problem related to how Microsoft uses these records in their products. Unless this has changed over the last year, Microsoft has a tendency to use long timeouts and appear to hang when attempting to find servers that may be behind firewalls pointed to by SRV records. This really means one must be careful about what zones are public that contain SRV records. There is also the issue that using a prefix precludes the use of a wildcard. As a result of these two problems, I doubt that SRV will displace MX record use.

MTAs would use

Is it useful (e.g. wrt 2821bis) to also have
for MSAs?

There are some MTA software packages that are using an SRV record to validate the EHLO and confirm that the MTA is authorized. The use of this record simplifies dealing with the public zone issue and is defined in:

The related software can be found at:


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