There are no such restrictions. Your claim is wrong. There is only a check for the syntactically correctness of email address according to the related RFC. Provide evidence for your claim.
@zopyx - thanks. I am not claiming there is a problem but there is something that's amiss and I am not quite sure.
I am trying to add some users with domain "globalreachtraining.services" and this is where it is causing a problem. I found the code where this is validated
RFC 2821 local-part: max 64 characters
RFC 2821 domain: sequence of dot-separated labels
characters allowed in label: A-Za-z0-9-, first is a letter
Even though the RFC does not allow it all-numeric domains do exist
but I don't want to tweak anything here foolishly. Thanks
As you found out (looking at the RFC), your email addresses should not pose a problem. Nevertheless, you apparently observe a problem. In those cases, debugging can help to find out what is going on. I am using Products.PDBDebugMode for such debugging. When Plone is started in "debug mode" (which is automatic if Plone is started in the "foreground", i,e. with the "fg" command) then an exception (or an log entry on level ERROR or above) enters the Python debugger where you can look around what went wrong.