MX DNS moving records

We are trying to move emails from our systems to a 3rd party system. I understand this is quite a simple process in that the MX record at our service provider needs to be changed to point to the 3rd party.
My question is this

If there is a backlog of emails waiting to be replied to at our end and the MX record is changed to point to the 3rd party. Is it still possible for us to reply to the backlog emails as the original mail address or would this fail due to DNS and reverse lookup?
i.e. mail sent to joe@abc.com arrives here, MX record changed can we still reply to mail as joe@abc.com?

thanks

I assume you mean that you're trying to move your incoming mail server? Yes, this is a relatively simple procedure; just change the MX records. Though bear in mind that the DNS change may take up to 24 hours (depending on the TTL of the MX record), so you'll need to think how you're going to get mail from your old mail server to your new mail server for sites that haven't updated yet over that 24 hour period.


No; I can't see why delivery would fail due to DNS. DNS doesn't restrict where you can send email from for a given domain. I could send an email from my server coming from your email address, and it would still arrive at its destination.