@stilgherrian it’s been a long time since I’ve admin’d a mail server in anger (always in anger… 
) but I have much recent experience when trying to interact with MTAs & other systems when using plain old plus-addressing that worked perfectly well for decades back when crusty greybeards (
honorary greybeard) ran the global infra
the most common / painful variants:
sign-up form accepts plus-address email & “completes” the process, but confirmation email never arrives (silently dropped somewhere in the pipeline, I have no way of knowing exactly where)
sign-up form has a (crappy) client-side “email address validation” with varying forms of incorrect / incomplete understanding of relevant RFCs, which can almost always be traced back in their web page code to crappy #regex that doesn’t match the full set of RFC-permitted chars
it’s been so painful that I’ve stopped using plus addressing all together & just reverted to a catch-all email config on my domains (which fortunately my mail provider supports well, I can reply from whatever email something comes in to), as well as masked emails using the provider’s domain depending on use case 
is a “small wrapper on regular expression matching functions regexpr and gregexpr to return the results in tidy data frames.” By 
We only managed by splitting their definition strings into multiple pieces that were assembled kind of like a puzzle. 
)
