Using the same email domain for both regular business email and high-volume marketing campaigns carries significant risk. Here are some major problems that can occur if your domain is used for EDM:

Business Email Disruption: If your domain is blacklisted due to EDM issues like spam complaints or infrastructure problems, this affects ALL mail sent from your domain. Legitimate customer and employee emails could be blocked, quarantined or spam-filtered.

Difficult Delist Process: Getting off email blacklists usually requires showing that problems are resolved and won't recur. This is much more difficult when the same domain is used for varying email types and volumes. De-listing requests may get rejected.

Increased Scrutiny: Once blacklisted, your domain will be under tight scrutiny. Any recurring issues with marketing emails can lead to re-listing, even stricter sanctions, or necessitate switching domains entirely.

Attribute Policies: Strict SPF, DKIM, and DMARC configurations help secure business email, but marketing email from external services may fail alignment. Overly tight policies could block or quarantine legitimate marketing mail.

Reputation Damage: Public blacklisting also damages sender reputation outside of just deliverability issues while blacklisted. Future emails from your domain may continually get filtered or land in spam unless major overhaul is done.

Sharing an email domain amplifies risks and fallout from potential email marketing problems. The safest approach is to use separate domains for each function and link them loosely at most.
For example:
@company.com - for regular business email communication
@company-edm.com - for high-volume email marketing campaigns