Hello @Markbert ,
A list upload that large may result in a list review, if there's enough new contacts (for your account) being added. If you are flagged for a list review, you'll need to speak with the Review team directly before you'd be able to send any emails.
For other general review info, please see our Community's Review FAQ.
As far as avoiding the deletion of contacts on other lists, my recommendation would be to upload your file of 30k contacts, and only add them to a newly created list specific for the email. That way, once the email has been sent, you can Delete the List and Contacts, which will only remove contacts not on other lists. For more info on this process, please see this article.
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