I can see from SMTP logs that some mail is being rejected
OutboundConnectionResponse SMTPSVC1 Sxxx – 25 – –
504+:+Helo+command+rejected:+need+fully-qualified+hostname 0 0
69 0 47 SMTP
In IIS6 > SMTP > Delivery > Advanced
I can see that the FQDN is set to the server name 'Sxxx'
This server hosts lots of different websites on different domains so I am not sure what this FQDN actually refers to? The server has no domain name of it's own, just IP addresses. The websites all have different domain names, so which one to choose.
As SMTP (AFAIK) just shunts out messages it has no real 'identity' itself: it's just given an email, looks at the recipient domain, finds the associated mx record and server and tries to pass the file/email to that server. Is my understanding here correct? If so, what should I do to provide a FQDN.
EDIT: just realised that the websites that send emails specify an actual external mail server, not localhost, so presumably they connect to the local SMTP service which passes the mail onto the specified external mail server (or does it bypass the local SMTP server completely and connect directly to the external mail server?) and it is that which actually sends the mail to the recipient (I'm missing some fundamental concepts here, I know) – so maybe the SMTP FQDN should be that of the external mail server?
If
Best Answer
The FQDN value found under
Delivery -> Advanced
in the SMTP server properties is the domain name that the SMTP Server uses when it has to identify itself to other mail servers.Most receiving MTA's will try to validate this identity by performing a reverse DNS lookup for the IP address of your sending server, so make sure the FQDN you input is also present in the PTR record for the public IP address of your server:
If you use the FQDN
mailserver01.neilthompson.tld
and your IP address is 1.2.3.4, make sure that the PTR record at4.3.2.1.in-addr.arpa
has a value ofmailserver01.neilthompson.tld
. Your ISP should be able to help you with this if you don't have authority of your own reverse zones