This actually happened to me when I was an intern (many years ago). My official job offer went to spam and I didn't see it until weeks later. Fortunately I happened to check the spam folder and saw it. I now make it a habit to regularly check the spam folder in Gmail and I often find non-junk mail in there.

Some universities recommend avoiding gmail accounts for application process precisely for this reason (I can't find the reference). My personal experience is that open source spam filters (spamassasin/rspamd) are far better at classifying spam than gmail's filter.

However, there is another reason why no one should use gmail for anything serious. There is always a risk that you may get shut out of your account without recourse, taking down access to other services along with it.