On incoming side of things:

In between your IP change, your script update your DNS record, and finally sender’s server gets the new IP address, you may lose emails coming to you. Most mail providers will eventually, at their chosen cadence and frequency, attempt to re-deliver the messages, so you might get them eventually on a delay. There is no way of knowing what you’re not missing in the event the sender’s server not retrying. Mails coming to you is delivered into folders per your configuration, and should not end up in spam because of your IP change.

On the outgoing side of things:

Every IP address has some reputation attached to it. Residential addresses tends to score lowly because of people getting virus/malware and become part of a bot net to spam. As you’ve got no control over the IP address you’d receive from your provider, there’s no guarantee if you will receive a clean IP or not. Worst case scenario here is you might end up with a blacklisted IP, and your mail never gets accepted (or silently discarded) by receiver’s mail server. You may also run into SPF record needing the IP address but you can probably get your DDNS script to update this as well or, maybe just use an A record.

If your intention is to receive emails, it might work, but you might miss a message or few.

If your intention is to send mails, it is cheaper and easier to just get a transactional mail provider and pay pennies per thousand mails, and never worry about it.

If your intention is to make a full fledged mail service with send and receive… it’s just not worth the hassle and headache.