You may experience not receiving emails even from a trusted contact. Here is some possible reason why.
If the email they are sending you is bigger than the available space of your email account, this email will be kept on your server’s mail queue and it will attempt to resend to your account every hour. We recommend checking your email account’s current available space. This is to prevent unnecessary email delivery failure.
Also, note that your email space is accounted for under the webspace or disk space of your hosting account. If your hosting account is full, all mails will be undelivered to any of your email accounts.
To free up space, you can delete emails that you no longer need and check your available storage space to avoid having issues. You can also get a much higher package to increase email or account storage. Check and compare packages for your Email Hosting.