Update email_mirror.py

[sravitha]

#10539

https://github.com/zulip/zulip/issues/10539

Testing plan:

GIFs or screenshots:

[timabbott]

@sravitha welcome! This change needs tests and screenshots from the /emails tool in the development environment to be considered.

Check out the Zulip commit message guidelines as well: https://zulip.readthedocs.io/en/latest/contributing/version-control.html#commit-messages

[zulipbot]

Heads up @sravitha, we just merged some commits that conflict with the changes your made in this pull request! You can review this repository's recent commits to see where the conflicts occur. Please rebase your feature branch against the upstream/main branch and resolve your pull request's merge conflicts accordingly.