Sending domain
What a sending domain is — the domain your mail claims to come from — and the SPF, DKIM and DMARC records that prove you control it before Sendly will send for it
A sending domain is the domain in the address your mail comes from —
yourcompany.com in hello@yourcompany.com. Before any platform sends on your behalf,
it has to establish that you actually control that domain, because the alternative is a
platform that will send mail claiming to be from anyone.
You prove it by publishing DNS records: an SPF record naming the services allowed to send for you, a DKIM key so signatures can be verified, and usually a DMARC policy saying what a receiving server should do with mail that fails both.
In Sendly
A project must have at least one verified sending domain before it can send anything, including through a compat endpoint. Verification is a DNS change, so it is the step in a migration whose timing you control least — start it first.
Guided DNS setup can publish the records for you and then keep checking them afterwards, which matters more than it sounds: a registrar migration or an unrelated edit that drops a DKIM record is otherwise discovered through a delivery failure weeks later.
See Verifying domains for the manual path and the record values.