The name in someone’s inbox is the first thing they judge you by, and it takes two minutes to get right.
Where
Go to Mollie Payments, then Email management. The sender settings are near the top.
Sender name
The from name your customer sees.
Use your business name. Not “WordPress”, not “admin”, not your own first name unless you are the brand.
Sender email address
The from address.
The plugin is clear about what this does: it overrides the default WordPress sender, and your customers will see this name and address in their inbox.
Use an address at your own domain
This matters more than it looks, and it is the difference between arriving and landing in spam.
If your website is yoursite.com, your sender should be something like info@yoursite.com.
Do not use a Gmail or Hotmail address. Mail servers check whether the sender is allowed to send on behalf of that domain, and a message from a Gmail address sent by your web server fails that check. Some providers will quietly bin it.
The admin email address
There is a separate field for this: where your own notifications go.
Use an address you actually read. A notification about a failed payment is worth nothing in an inbox nobody opens.
Test it
There is a Send test email button, and the plugin explains what it does: it sends a short test to the admin address above, so you can check that your sender settings arrive correctly.
Press it. Then go and look at the email in a real inbox.
Check three things. Does the sender name look right? Did it arrive in the inbox rather than spam? Would you trust it if you did not know who you were?