It is possible in all standard emails to set an expiry date, after which time if the email has not been opened then it will get automatically deleted from your inbox. It is good practice to set the expiry date on time sensitive emails, so as not to clog up the recipients mailbox with messages which become irrelevant after a certain cutoff time - such as time limited special offers, or invites to meetings, etc.
Had your missing old emails ever been read, or were they unopened ?
