On Wed, Dec 20, 2017 at 7:21 AM, alister via Python-list <python-list@python.org> wrote: > On Mon, 18 Dec 2017 07:57:27 +1100, Ben Finney wrote: >> A more correct match would boil down to: >> >> * Match any printable Unicode characters (not just ASCII). >> >> * Locate the *last* ‘@’ character. (An email address may contain more >> than one ‘@’ character; you should allow any printable ASCII character >> in the local part.) >> >> * Match the domain part as the text after the last ‘@’ character. Match >> the local part as anything before that character. Reject an address >> that has either of these empty. >> >> * Validate the domain by DNS request. Your program is not an authority >> for what domains are valid; the only authority for that is the DNS. >> >> * Don't validate the local part at all. Your program is not an authority >> for what local parts are accepted to the destination host; the only >> authority for that is the destination mail host. > > At which point you have basicaly boiled your test down to > <Anything>@<anything>.<anything> which is rather pointless
Not quite. Firstly, I would exclude all whitespace from your matchable characters; even though technically you CAN have spaces in email addresses, that'll almost never happen, and it's a lot more common to delimit with whites. Secondly, there's actually no requirement to have a dot in the domain part (and Ben never said so). However, you can straight-forwardly validate the domain by attempting a lookup. rosuav@sikorsky:~$ dig +short mx ntlworld.com 1 mx.tb.ukmail.iss.as9143.net. 1 mx.mnd.ukmail.iss.as9143.net. rosuav@sikorsky:~$ dig +short mx benfinney.id.au 10 in1-smtp.messagingengine.com. 20 in2-smtp.messagingengine.com. rosuav@sikorsky:~$ dig +short mx dud.example.off.rosuav.com rosuav@sikorsky:~$ If there are no MX records for a domain, either the domain doesn't exist, or it doesn't receive mail. (Remove the "+short" for a more verbose report, in which case the failure state is a return code of NXDOMAIN.) > there are only 2 reasons why you would want an email anyway > > 1) Data mining, just to add to your mailing list- in which case even if > it validates you still don't know if it is a fake address to prevent spam > so validating is pointless > > 2) it is part of a registration process, in which case if it is incorrect > the registration email will not be received & registration cannot be > completed so self validating without any effort. 3) You're building a text display system (forum posts, text chat, etc, etc) and want to have web links and email addresses automatically become clickable 4) You ask a user to provide "contact information". If s/he provides an email address, you automatically send emails; if a phone number, you automatically send SMS/text messages; otherwise, you leave it up to a human to contact the user. Plenty of possibilities beyond those two. Don't assume there's nothing else that can be done just because your imagination can't come up with anything :) ChrisA -- https://mail.python.org/mailman/listinfo/python-list
