What setting when mx records are hosted elsewhere

Hi I’m hosting a website for a customer who manage their own domain name and email accounts so they changed the A-records to point to my server where the new wordpress site is and they manage their own MX records.

I’m using Contact Form 7 but this wont send to [email protected] as I’m not hosting their emails.

How do I get around this? I assume it must be a common issue.

Any help would be much appreciated. Thanks

https://www.ads-software.com/plugins/contact-form-7/