Single-quoted email addresses in message headers causing problems

One of our users has received an email which has a number of single-quoted addresses in the "To:" header (as well as other addresses), like this:

To: Some One <[email protected]>,
    "[email protected]" <[email protected]>,
    "'[email protected]'" <'[email protected]'>,
    "'[email protected]'" <'[email protected]'>,

When our user tried to reply-all, the email was rejected by our mailserver with a response of "501 5.1.3 Bad recipient address syntax".

My understanding of RFC 5322 (which obsoletes RFCs 2822 and 822) is that a single quote (') is valid in the local part of an email address (before the "@"); e.g. as an apostrophe in an address like "o'[email protected]". However it is not a valid character to use to quote the whole address, and therefore the addresses above are not syntactically correct, and our mailserver was right to reject the reply.

I have a number of questions:

1. Am I correct in my understanding that these addresses are invalid?
2. Which system has responsibility to prevent a message with invalid addresses in the header being sent? The sender's user agent (Outlook, whatever)? The mailserver the user agent submits the message to? Our mailserver?
3. I suspect that the sending SMTP server was MS Exchange; is there a known issue that allows addresses like these?

Depending on the answers to those questions, I expect I'll submit one or more bug reports (to vendors and/or administrators of the sending mailserver), as well as advising our user to remove the single quotes before replying. Any other suggestions for this situation?