SRV DNS records allow the use of DNS for publishing services and service discovery. Their main use is to allow services to run easily on non-standard ports and to reduce the configuration burden when setting up clients.
A SRV record has the following form:
_Service._Protocol.Name. TTL Class SRV Priority Weight Port Target
Service: the symbolic name of the service.
Protocol: the transport protocol of the service; this is usually either TCP or UDP.
Name: the domain name terminated with a . for which this record is valid - often omitted in DNS shorthand which then
defaults to the zone name.
TTL: standard DNS time to live field.
Class: standard DNS class field (this is always
IN for Internet).
Priority: the priority of the target host, lower value means more preferred.
Weight: A relative weight for records with the same priority.
Port: the TCP or UDP port on which the service is to be found.
- Target: the canonical hostname of the machine providing the service.
Yours appears an example of an autodiscovery service :) pointing to
TCP port 443 on the aptly named host
One such autodiscovery service seems to be used in automatically configuring MS Outlook but that may not be the only use-case.