There is a specific email that i want for it to be received in real-time with no delay so i want this email or to be more specific and more secure i want the email domain ip to be skipped from spam and virus checking and any process that can prevent it from reaching the inbox in real time and in the same time prevent spoofing so i want the ip to be skipped instead of the domain, because i receive alot of important emails from that domain
You could whitelist the domain / email address so that it is not processed for spam or virus. You could also bypass greylisting so that the incoming email hits the mailbox immediately, in real time, to use your words.
Spoofing can be prevented via SPF in your DNS records. The default SPF is liberal, you could make it more strict.
greylisting is the only antispam feature that will delay mail in a system with sufficient resources and reasonable spam/AV configuration, and that’s usually by a few minutes, not a day (but it’s up to the sending mail server how soon they requeue).
You should make sure you’re not doing something pathological, like running the non-daemon versions of SpamAssassin or ClamAV. In the former case, it’d slow mail by a lot, in the latter case, it is potentially catastrophic (potentially triggering the oomkiller every time you get a bunch of mail queued up).
ClamAV is extremely resource intensive, in general, and should only be used if you have plenty of resources to give it, mostly memory…but it’s also more CPU intensive than you might expect.
All that said, don’t guess! Actually look at your maillog to see why mail delivery is slow! We cannot really guess either. You could have something else entirely going on. All sorts of reasons mail can be slow and it sounds like you’re just guessing it is spam/AV scanning (which is not an unreasonable guess, but don’t guess!).