Proxies, by definition should be completely transparent. Software should
not be aware that a proxy is involved in the middle (except, perhaps, for a
simple proxy on/off setting).
Reverse proxies by definition hide URLs behind other URLs.
Is there is reason why webmail always outputs absolute URLs?
Yes. Various bugs in some browsers with relative HTTP redirect URLs.
And dont forget RFC2068 :)
Location = "Location" ":" absoluteURI
The absolute URL should be configurable at runtime, not hardcoded. This
will fix the problem.
If you have 'UseCanonicalName On' in httpd.conf (default) then
SQWebmail uses the ServerName there for self-referencing url's.
If you set 'UseCanonicalName Off' then SQWebmail (or any other
CGI) will use the HTTP-Host-header as supplied in the request.
The simple solution will be 'UseCanonicalName Off' in httpd.conf,
or set the ServerName to the hostname of the reverse-proxy and
'UseCanonicalName On' for compatibility with broken browsers or
if your reverse-proxy adds a new host-header (like mod_proxy...)
Both servers have to use either plain HTTP or SSL.