What is My Domain in Salesforce and why does it matter?

My Domain is a custom subdomain for your Salesforce org — acme.my.salesforce.com instead of the generic na123.salesforce.com. As of recent releases, My Domain is required for every production org — Salesforce no longer lets you turn it off.

Why it matters:

1. SSO and Identity — SAML and OAuth flows require a stable URL to redirect to. My Domain provides that.
2. Security — the .lightning.force.com URL pattern (which My Domain enables) is a key part of how Salesforce isolates Lightning component sessions and applies CSP policies.
3. Branding — login pages can be branded with the company logo, colours, custom domain.
4. Permission features — features like Login Hours, IP Restrictions, and certain MFA flows require the My Domain URL.
5. Deployment — sandbox URLs, Connected App callbacks, and integrations all reference My Domain consistently.

Setting it up: Setup -> My Domain -> register a name -> deploy to users -> optionally redirect old URLs. Once deployed, you can also set policies like "prevent login from non-My-Domain URLs" which closes off legacy access patterns.

Admins inheriting older orgs sometimes find My Domain not yet deployed or in a half-rolled-out state — surfacing that and finishing the migration is often a quick win.