Re: [PATCH v3 1/3] send-mail: improve checks for valid_fqdn

Aditya Garg <gargaditya08@live.com> writes:

Is it a common misconfiguration in the first place that singling out a name ending with double dots (which indeed is very likely that nobody should be relying on getting accepted by sensible SMTP servers, hence very safe tightening) is worth doing? If MacBooks as shipped would by default claim to be "MacBook.." like your example had (I do not know if that is the case, as I do not live in Apple ecosystem), it may give us a reason to special case the trailing double-dots, for example.

I personally feel that "run of at most 63 alnum or dash separated by a single dot in between" is easy enough to explain, so if I were doing this change, I would just use the regexp used in posted patch [*] and if nobody complains, stop right there. If we get any complaint, then I'd detect and reject the case where the string ends with double-dots.

[Footnote]

 * ... but I don't know if your use of negative lookaround
   assersions is correct.  Shouldn't the "a label cannot begin or
   end with dash" be applied not just to the first label but
   consistently to all of the dot-separated labels?