If you change one thing about how you send, make it this. Sending from a mailbox on a domain you control is what lets you configure authentication, build a reputation that belongs to you, and look like a real business to the person receiving the email.
What you gain
| Free consumer address | Business mailbox on your domain | |
|---|---|---|
| SPF, DKIM, DMARC | Cannot be configured by you | Fully under your control |
| Reputation | Shared with millions of accounts | Yours, and it accumulates |
| Sending limits | Lower — 250 / 350 / 450 a day per market by plan | Higher — 250 / 500 / 1,000 a day per market by plan |
| Recipient trust | Looks personal or unofficial | Recognisable as your business |
| Reply handling | Personal inbox | Can be a shared or monitored mailbox |
A useful pattern
Some businesses send outreach from a subdomain, such as mail.yourbusiness.com, so that a problem with campaign email does not affect the reputation of the domain carrying their day-to-day correspondence. This is worth considering once you are sending consistently, and it requires the same authentication setup on the subdomain.