Answer:
It depends. (OPINION)
Explanation:
If this is an important email, and it REALLY had to be sent the day of, then yes, it may be appropriate to call the day of. However, if you procrastinated until the last day and are really worried; well; that's your fault. At least wait a day and give the receiver some time to process; they could be really busy. At least that's how I view it.
