There are several reasons why a business may want to email from a subdomain:
Branding: Emailing from a subdomain allows a business to establish a separate, distinct identity for its email communications, which can help to build trust with recipients and increase the likelihood that emails will be opened and read.
Reputation management: By using a subdomain, a business can protect the reputation of its main domain. If there are any issues with email deliverability or engagement, they will be isolated to the subdomain, which helps to maintain the reputation of the main domain.
Segmentation: Emailing from a subdomain allows a business to maintain relevance with its various list segments. Segments receiving emails from a relevant subdomain will increase overall effectiveness of marketing campaigns.
Deliverability: Emailing from a subdomain can improve email deliverability as ISPs may have a better understanding of the emails source and sender, and will be more likely to deliver the emails to the inbox rather than the spam folder.