Where the sender name and address for each email identity live, and why actual delivery depends on your server configuration.
Magento strictly separates the sender identity (the name + email address shown in the "From" field) from the technical delivery path of the email.
Store Email Addresses
Under Stores > Configuration > General > Store Email Addresses you maintain up to five named identities: General Contact, Sales Representative, Customer Support, plus two freely nameable Custom Email 2 and Custom Email 3. Each consists of a name field and an email address field.
Assigning identities to email types
In the respective configuration sections (Sales Emails, Customer Configuration, Newsletter) you pick via a dropdown which of these five identities is used as the sender for that email type – e.g. "Sales Representative" for order confirmations, "Customer Support" for password reset emails. That way customers can tell at a glance from the sender name what an email is about, without reading the subject line.
Store view scoping
All five identities are configurable per store view – a bilingual store can use "Kundenservice" in its German store and "Customer Support" in its English store, each with a matching sender address, without needing separate templates.
Actual delivery: sender address isn't the same as deliverability
Important to understand: this configuration only determines what shows up in the email's "From" field – not whether the email actually gets delivered. Magento itself doesn't run its own mail server; it hands emails off to whatever PHP mail() function or configured SMTP transport your hosting/server operator has set up. For receiving mail servers (Gmail, GMX, Outlook) not to flag the email as spam, the actually sending domain needs valid SPF and ideally DKIM records – simply changing the sender address in the backend without matching DNS records can mean emails are "sent" but never delivered. If deliverability problems persist, switching to a dedicated transactional email service instead of the server's own mail sending is worth considering.