Rackspace Email is a hosted mailbox service for small businesses, sold directly and through many web hosts and resellers. Its infrastructure runs under the emailsrvr.com name, so Spaw reports these domains as mx_provider: "rackspace" even though rackspace.com itself, the company's corporate domain, is hosted on Microsoft 365.
How Rackspace shows up in DNS
Rackspace Email asks customers to publish exactly two MX records, mx1.emailsrvr.com at priority 10 and mx2.emailsrvr.com at priority 20, and no others. Spaw matches the .emailsrvr.com suffix. Rackspace is a mailbox host: the MX target stores the mail, mx_found is true and mx_implicit is false. Hosted Exchange customers at Rackspace use different records and are classified by whatever their MX points at.
How Rackspace answers a verification handshake
Rackspace Email typically rejects unknown recipients at RCPT TO, so most checks settle on the first attempt. The admin control panel lets a domain owner configure a catch-all mailbox, and domains with one answer as catch-all. Rackspace's inbound servers also apply rate limits and reputation checks, and a probe from a source they have not seen is occasionally deferred.
What that means for your verdicts
Expect deliverable with mailbox_exists: true or undeliverable with reason: mailbox_not_found and smtp_reason: no_mailbox for most domains, and risky with reason: catch_all for the ones with a catch-all mailbox. For catch-all domains Spaw returns mailbox_confidence; Rackspace is not on the established-provider list, so the estimate depends on the domain's DMARC and SPF, its age, the username's shape and your own delivery data. There are no consumer username rules for Rackspace domains, since every Rackspace domain is a customer's own domain.
Rackspace's customers are small businesses, and their address lists carry many role inboxes: info@, office@, sales@. Spaw flags them risky with reason: role even when the handshake confirms they exist. Staff turnover shows up as mailbox_not_found once the account is deleted, and the address then joins your suppression list.
SPF and DMARC at Rackspace
Rackspace's documentation asks domain owners to publish v=spf1 include:emailsrvr.com ~all when Rackspace Email is the only sender, and to enable DKIM from the control panel; any other service sending as the domain needs its own include. Spaw reports the live state in has_spf and dmarc_policy, and a company domain without SPF adds ten risk points to its addresses.
Practical notes for sending to Rackspace users
Because most Rackspace domains belong to small companies that manage DNS through a web host or reseller, SPF and DMARC are frequently missing or misconfigured on the receiving side, which affects their own deliverability but not yours. On your side, an aligned sending domain and a clean list are enough; Rackspace's filtering is conventional. Re-verify these lists on a schedule, since small-business staff and role inboxes change often.
For a live look at any Rackspace-hosted domain, run it through the free MX lookup and the SPF and DMARC checker.