There are some good reasons to have multiple sender subdomains, and this is the perfect opportunity to create them.
Many ISPs recommend separate domains for separate email types (e.g. for customer acquisition campaigns, customer lifecycle campaigns, and operational emails) so that your sending behavior is consistent per domain.
You can have different domains per brand, language, or even department.
Tip: It is not recommended to define a separate domain, for sending fewer than 40-50,000 emails per month.
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SAP Emarsys DNS Settings
Marketing and transactional subdomains – should we make the separation?