Can we use a custom URL to send an email to the instance?
Release or Environment
The custom URL is only for the URL hostname. The ServiceNow POP3 mailbox name will not change i.e firstname.lastname@example.org.
If you would like to send it to a different address, you would need email admin to set email redirection to the instance email address or just set up your own POP3 or IMAP server instead of/in addition to the ServiceNow POP3 email account