Hi kdswim,
welcome to the Apple (user-to-user) Community!
Re: "I am not getting an email from a specific sender : they are important and not spam"
Wondering if you need to check that the college has your current, correct, email address.
Eg: If not, the emails would likely be returned as "undeliverable" to the college.
You could check that the college email address is listed on a card in your Contacts app.
It is possible messages from people not listed in your contacts could be blocked or hidden
ie: using a setting, a filter, or a "rule".
Else: you might want to check through the Mailboxes you have ... eg: once found some valuable emails that were addressed to multiple people were ending up in a folder called "Bulk"
... if you have more than one email account ... there may be extra "Bin" or "spam" folders besides the usual "junk" folder to check.
You could also try a search of your email for messages from the college to see if you find them:
Search for emails in Mail on Mac - Apple Support
All the best :-)