incoming email addresses - some have double contents and backslashes?

I'm not even sure how to title this - in our app we can receive emails, and we are parsing the to email address.

we are logging the address like this functions.logger.info('Parsing email address: %j', addr);

most of the emails come in as a string, like this:
"Parsing email address: "example_12345@mail.exampleapp.com""

but today we started some receiving addresses like this:

Parsing email address: "\"example_78910@mail.exampleapp.com\" <example_78910@mail.exampleapp.com>"

Has anyone seen this before? It's as if the mail client is formatting the data in an unusual way before sending it to us. Can anyone give some pointers on what's happening here, or what mail client might be the culprit (if that's even the case)?

Thanks!

That's within the spec of [RFC 5322]
(https://datatracker.ietf.org/doc/html/rfc5322#section-3.4)

> Normally, a mailbox is composed of two parts: (1) an optional display
name that indicates the name of the recipient (which can be a person
or a system) that could be displayed to the user of a mail
application, and (2) an addr-spec address enclosed in angle brackets("<" and ">"). There is an alternate simple form of a mailbox where
the addr-spec address appears alone, without the recipient's name or
the angle brackets. The Internet addr-spec address is described in
section 3.4.1.

It goes on to mention some other common formats for the To: header you might want to handle.