[namibj]

I thought DMARC/DKIM was necessary for delivering to Gmail for years now; in any case, there should be few who can't use a backup email to subscribe, as your newsletter won't be the only thing that has these anti-spoof requirements.

[viraptor]

Not necessary. Just very highly recommended. I can still deliver my cron emails from a rando host successfully.

[namibj]

That doesn't rule out DKIM, which only requires the `From:` header's domain to list a pubkey and the email to include a DKIM signature from a matching private key. SPF is the one that regulates which hosts a domain's outbound SMTP servers are on.