Hi Tim, > Turned out the local part of the email address was case sensitive. She > had no idea this was the case, and it's the first time I've ever > (knowlingly) encountered this. Looking at the email headers, they're > using a Microsoft Exchange SMTP server. For the low-down: > > https://stackoverflow.com/questions/9807909/are-email-addresses-case-sensitive
I disagree with the final conclusion of the top-scoring answer there. The case of the username part does matter. :-) It starts okay, explaining the why. Email started within a machine. The ‘address’ was just the username. Usernames are case sensitive on many systems, including Unix. When passing email between machines was added, e.g. the routing path eclipse!inputplus!ralph, the host at each hop deleted itself from the start of the list and passed it on downstream. The only interpretation of the username part was by the final hop. As DNS didn't exist, a table of hostname to network address for the world was centrally maintained and shared, called HOSTS, stored locally on Unix as /etc/hosts. RFC 810 says hostnames are drawn from A-Z plus punctuation and never uses lowercase, probably because some interfaces still couldn't render it at the time. Unix's preference for lowercase is probably why the hostname look-up became implicitly case-insensitive. Maintaining a worldwide /etc/hosts-equivalent was tedious and DNS was born; it preserved the case-insensitivity. Routing email explicitly was a nause and with DNS the switch to email delivery with DNS A and MX records allowed just the username@final.destination, but both halves maintained their original semantics: case sensitive before the at-sign, insensitive afterwards. Unix mail servers gradually started to handle non-Unix email senders on other platforms failing to use the correct email address, e.g. Sendmail has an F=u flag related to case-conversion. By working around the problem, they help propagate it. Postel got it wrong. :-) I'm a customer of a financial institution that insists on sending emails to capitalised addresses, e.g. freda.blo...@example.com. -- Cheers, Ralph. -- Next meeting: BEC, Bournemouth, Tuesday, 2020-01-07 20:00 Check to whom you are replying Meetings, mailing list, IRC, ... http://dorset.lug.org.uk/ New thread, don't hijack: mailto:dorset@mailman.lug.org.uk
