With gmail you can only auto-forward mail to mailboxes which you can prove you own / have access to (by responding to an email challenge generated by google, sent to that mailbox). This meant that I couldn't automatically forward receipts / invoices from e.g. Airbnb, Digital Ocean, Microsoft etc., to Expensify. So I have a cron job that logs into my gmail account every night at 2am, scans for new mail matching certain criteria, and manually forwards it to Expensify's mailbox.

Now I don't have to remember to forward mail to Expensify every time I book an airbnb for business travel, or pay my monthly O365 subscription.

It works great, except for when a company decides to change the format of their emails and I have to update my script to use a new search pattern.