## Type of Change
- [x] Bug fix
## Description
Closes#13119
The current IMAP connector uses `split(',')` to parse email headers,
which crashes when a sender's display name contains a comma inside
quotes (e.g., `"Doe, John" <john@example.com>`).
This PR replaces the manual string splitting with Python's standard
`email.utils.getaddresses`. This correctly handles RFC 5322 quoted
strings and prevents the `RuntimeError: Expected a singular address`.
## Checklist
- [x] I have checked the code and it works as expected.
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Co-authored-by: Kevin Hu <kevinhu.sh@gmail.com>
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