A custom sending domain is a domain you control (for example yourbrand.com) that you configure to send outgoing email, so messages arrive from an address like quotes@yourbrand.com instead of a generic no-reply address on a shared platform domain. To make it trustworthy to inbox providers, you add DNS records that authenticate it: SPF, DKIM, and DMARC. Together these prove the mail genuinely came from you and were not spoofed.
How it works
You point a domain (or subdomain) at your sending platform through DNS records. SPF lists which servers are allowed to send for the domain. DKIM adds a cryptographic signature that receivers verify against a published key. DMARC ties the two together and tells inbox providers what to do when a message fails, plus where to send reports. Once these pass, mailbox providers like Gmail and Outlook are far more likely to place your mail in the inbox rather than spam.
Why it matters
Quotes, order confirmations, and follow-ups only work if the buyer actually sees them. Mail sent from a generic platform address is easier to filter, and it looks less credible to a purchasing manager comparing vendors. A properly authenticated domain improves deliverability and reinforces that the quote is really from your business. Gmail and Yahoo now effectively require authentication for anyone sending at volume, so this is table stakes rather than a nice-to-have.
Example for Shopify B2B quoting
Say a wholesale buyer requests pricing through your store. With a custom sending domain, the Live Quote link lands from quotes@yourbrand.com, matching your storefront and your team’s email. That consistency raises open and reply rates and keeps the whole exchange on your brand instead of a third party’s. See pricing for which plans support sending from your own domain versus link or PDF delivery.