CNAME

[Dan Lukes]

Dalibor Toman wrote:

> > RFC 2821 mimo jine popisuje zpusob nalezeni serveru na ktery ma byt
> > posta odeslana a povoluje CNAME....
> 
> samozrejme, ze mam na mysli MX ukazujici na CNAME...

[3.6]:
-----------------
Only resolvable, fully-qualified, domain names (FQDNs) are permitted
when domain names are used in SMTP.  In other words, names that can
be resolved to MX RRs or A RRs (as discussed in section 5) are
permitted, as are CNAME RRs whose targets can be resolved, in turn,
to MX or A RRs.  
-----------------

a, podrobneji, kapitola [5]:
-----------------
The lookup first attempts to locate an MX
record associated with the name.  If a CNAME record is found instead,
the resulting name is processed as if it were the initial name.  If
no MX records are found, but an A RR is found, the A RR is treated as
if it was associated with an implicit MX RR, with a preference of 0,
pointing to that host.  
-----------------


	Tedy MX, A a CNAME jejichz vysledkem je MX nebo A. o MX ukazujicim na
CNAME jsem tam nenasel nic. Ostatne, MX smerujic na CNAME je nemozne
proto, ze vyskyt CNAME na prave strane v DNS zakazuji RFC tykajici se
DNS, takze takovy zaznam je vadny.



A puvodnimu tazateli:
	Pouzivani CNAME na prave strane "@" je sice teoreticky mozne, ale z
ruznych, do znacne miry historickych, duvodu muze byt problematicke
(ostatne, projevy jste zaznamenal sam). Proc misto CNAME nepouzijete
proste MX, ktere na to je delane ?

							Dan


-- 
Dan Lukes      tel: +420 2 21914205, fax: +420 2 21914206
root  of FIONet,  KolejNET,  webmaster  of www.freebsd.cz
AKA: dan na obluda.cz, dan na freebsd.cz, dan na kolej.mff.cuni.cz