Re: [Exim] Trailing dots in HELO domain

In article <E16LkU1-0002kb-00@???>,
Dogulas Gray Stephens <DGrayStephens@???> wrote:
>
>I am afraid that this is an off topic, however I was hoping that
>someone could clarify on the SMTP standards (so RFC2822) and trailing

YM RFC822. RFC2822 is a proposed standard protocol.

>dots in a DNS name during a helo statement.
>
>Normally in DNS a trailing dot forces the resolution to start at the
>root

RFC1123 6.1.4.3 says that if an abbreviation method is provided (eg. a
search path or alias list) then there must be some convention for
denoting that a name is already complete. A trailing dot is given as
an common method, but that notation is not actually required by the RFC.

Note that section 6.1.4 is about the _user interface_ (ie. between the
resolver library and the application program) and not about the
specification of domain names.

Domain names are defined in RFC1035:

<domain> ::= <subdomain> | " "
<subdomain> ::= <label> | <subdomain> "." <label>
<label> ::= <letter> [ [ <ldh-str> ] <let-dig> ]

This was relaxed slightly by RFC1123 to allow labels with a leading
digit, however, as you can see, empty labels are not allowed, and
therefore a trailing dot is a syntax error.

>Is it legal for an MTA to send the trailing dot in a helo statement,

No.

Peter