E-mail Sending - Sendgrid?

I’m an e-mail domain administrator and I watch my DMARC reports. My DMARC policy is set to quarantine, rather than reject. My eventual goal is to set it to reject, but I need to track down everyone who is sending e-mail on behalf of our domain.

I’ve noticed that I’m getting a lot of quarantined messages with header_from=<my domain> and envelope_from=sendgrid.net.

The only thing I can think of is maybe Doxy.me’s premium direct-from-browser send method is using Sendgrid. Does it “pretend” to send e-mails on behalf of my domain?

Can someone from Doxy confirm this and/or let me know what I should set my DMARC policy to?

Here is an example parsed DMARC report:

{
  "org_name": "google.com",
  "org_email": "noreply-dmarc-support@google.com",
  "org_extra_contact_info": "https://support.google.com/a/answer/2466580",
  "report_id": "x",
  "begin_date": "2021-02-14 00:00:00",
  "end_date": "2021-02-14 23:59:59",
  "errors": [],
  "published_policy": {
    "domain": "mydomain.com",
    "adkim": "s",
    "aspf": "s",
    "p": "quarantine",
    "sp": "quarantine",
    "pct": "100",
    "fo": "0"
  },
  "source_ip_address": "168.245.66.189",
  "source_country": "US",
  "source_reverse_dns": "xvfrqnbd.outbound-mail.sendgrid.net",
  "source_base_domain": "sendgrid.net",
  "message_count": 6,
  "disposition": "quarantine",
  "spf_aligned": false,
  "dkim_aligned": false,
  "passed_dmarc": false,
  "header_from": "mydomain.com",
  "envelope_from": "sendgrid.net",
  "dkim_results": [
    {
      "domain": "sendgrid.net",
      "selector": "smtpapi",
      "result": "pass"
    }
  ],
  "spf_results": [
    {
      "domain": "sendgrid.net",
      "scope": "mfrom",
      "result": "pass"
    }
  ]
}