How do you check suspicious emails?

hi ,
I would like to know how you check suspicious mails (also with attachments or links)?
Thanks to our mail proxy, we can intercept quite a lot, but sometimes there are e-mails where I am unsure and would like to check them before I release them.
(I would be interested in technical solutions or procedures, e.g. sandbox (if so what))
We have all our solutions onprem.
Thank you for your help

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