|Don't ask to ask, just ask|
Having just skimmed the parts of RFC 2822 regarding e-mail addresses, it was pretty clear that "accept email address that have a period before @ in violation of the RFC" isn't based on the copy that I found. It clearly went to some length to document how you can use period before the @ so I'd be quite to surprised to find that some other part of the RFC disallowed such usage.
As for ignoring case before the @, I wrote above:
Yes, I realize that it is possible to set up a system such that ExpertsExchange@example.com and ExpertSexchange@example.com are completely separate addresses, but anybody who does that deserves to suffer from such a set-up.
which I think makes my position on that quite clear. Note that I certainly won't be altering case of the user portion of any addresses (I see no reason to alter case of any potion of the address, actually, but I realize that altering the case of the user portion is at least technically allowed to break the e-mail address).
As for firstname.lastname@example.org%bar.com, I agree that this is a valid e-mail address and can see uses for it in certain situations. But I also feel that requiring such an address format be used by your (internal or external) customers when they request that e-mail be sent to them by random external entities is a good reason to demand a new e-mail service provider. So I don't yet feel guilty about considering not allowing such addresses to be used in order to register for a service we provide on the internet (as my regex above disallows). So (at this point) I won't have a problem with comparing such addresses.
As for a pick-and-choose module, one reaction I have is that I think it took me less than 10 minutes to cut'n'paste from two RFCs to come up with my simplistic results that seem amply permissive to real-world e-mail addresses meant to be used "at large". So I don't foresee it as particularly difficult to spend 10 minutes to pick and choose the items that fit one's specific situation. And part of my point was to wonder why people seem to never bother to cut'n'paste from the RFCs when they go to roll their own regexes.
But I will certainly consider producing such a module (or patching an existing module, or, rather, trying to patch an existing module since CPAN so very often makes usefully patching existing modules difficult and extremely slow), especially as more details of what items are likely to be worth picking and choosing between are explained to me explicitly and clearly. I don't claim to be an expert on e-mail addresses, in fact, part of the point of posting this was my shock at how easy it appeared to be to provide something that seemed more practical (for the very common problem of validating e-mail addresses being entered by users of a web page) than what my coworker reported finding on CPAN.
Is "do not accept email address that require an open relay to work" nothing more than "don't allow % after the @"? In any case, thanks for another justification for not using full-RFC-2822 addresses.
Thanks also for you assessment of whether this would be a good addition to CPAN. I appreciate your opinion.